diff --git a/fpdfsdk/formfiller/cffl_combobox.h b/fpdfsdk/formfiller/cffl_combobox.h
index 7d5a38e..dc8441d 100644
--- a/fpdfsdk/formfiller/cffl_combobox.h
+++ b/fpdfsdk/formfiller/cffl_combobox.h
@@ -19,7 +19,8 @@
   CFX_WideString sValue;
 };
 
-class CFFL_ComboBox : public CFFL_TextObject, public IPWL_FocusHandler {
+class CFFL_ComboBox : public CFFL_TextObject,
+                      public CPWL_Wnd::FocusHandlerIface {
  public:
   CFFL_ComboBox(CPDFSDK_FormFillEnvironment* pApp, CPDFSDK_Widget* pWidget);
   ~CFFL_ComboBox() override;
@@ -45,7 +46,7 @@
   bool IsFieldFull(CPDFSDK_PageView* pPageView) override;
 #endif
 
-  // IPWL_FocusHandler:
+  // CPWL_Wnd::FocusHandlerIface:
   void OnSetFocus(CPWL_Edit* pEdit) override;
 
  private:
diff --git a/fpdfsdk/formfiller/cffl_formfiller.cpp b/fpdfsdk/formfiller/cffl_formfiller.cpp
index f405e35..e59cd05 100644
--- a/fpdfsdk/formfiller/cffl_formfiller.cpp
+++ b/fpdfsdk/formfiller/cffl_formfiller.cpp
@@ -37,8 +37,7 @@
 void CFFL_FormFiller::DestroyWindows() {
   for (const auto& it : m_Maps) {
     CPWL_Wnd* pWnd = it.second;
-    CFFL_PrivateData* pData =
-        static_cast<CFFL_PrivateData*>(pWnd->GetAttachedData());
+    auto* pData = static_cast<CFFL_PrivateData*>(pWnd->GetAttachedData());
     pWnd->InvalidateProvider(this);
     pWnd->Destroy();
     delete pWnd;
@@ -359,7 +358,7 @@
     CPWL_Wnd::CreateParams cp = GetCreateParam();
     cp.pAttachedWidget.Reset(m_pWidget.Get());
 
-    CFFL_PrivateData* pPrivateData = new CFFL_PrivateData;
+    auto* pPrivateData = new CFFL_PrivateData;
     pPrivateData->pWidget = m_pWidget.Get();
     pPrivateData->pPageView = pPageView;
     pPrivateData->nWidgetAge = m_pWidget->GetAppearanceAge();
@@ -384,18 +383,17 @@
     return;
 
   CPWL_Wnd* pWnd = it->second;
-  CFFL_PrivateData* pData = (CFFL_PrivateData*)pWnd->GetAttachedData();
+  auto* pData = static_cast<CFFL_PrivateData*>(pWnd->GetAttachedData());
   pWnd->Destroy();
   delete pWnd;
   delete pData;
-
   m_Maps.erase(it);
 }
 
-CFX_Matrix CFFL_FormFiller::GetWindowMatrix(void* pAttachedData) {
+CFX_Matrix CFFL_FormFiller::GetWindowMatrix(CPWL_Wnd::PrivateData* pAttached) {
   CFX_Matrix mt;
-  auto* pPrivateData = reinterpret_cast<CFFL_PrivateData*>(pAttachedData);
-  if (!pAttachedData || !pPrivateData->pPageView)
+  auto* pPrivateData = static_cast<CFFL_PrivateData*>(pAttached);
+  if (!pPrivateData || !pPrivateData->pPageView)
     return mt;
 
   CFX_Matrix mtPageView;
diff --git a/fpdfsdk/formfiller/cffl_formfiller.h b/fpdfsdk/formfiller/cffl_formfiller.h
index b9af389..e9c2c55 100644
--- a/fpdfsdk/formfiller/cffl_formfiller.h
+++ b/fpdfsdk/formfiller/cffl_formfiller.h
@@ -19,7 +19,8 @@
 class CPDFSDK_PageView;
 class CPDFSDK_Widget;
 
-class CFFL_FormFiller : public IPWL_Provider, public CPWL_TimerHandler {
+class CFFL_FormFiller : public CPWL_Wnd::ProviderIface,
+                        public CPWL_TimerHandler {
  public:
   CFFL_FormFiller(CPDFSDK_FormFillEnvironment* pFormFillEnv,
                   CPDFSDK_Widget* pWidget);
@@ -84,8 +85,8 @@
   void TimerProc() override;
   CFX_SystemHandler* GetSystemHandler() const override;
 
-  // IPWL_Provider
-  CFX_Matrix GetWindowMatrix(void* pAttachedData) override;
+  // CPWL_Wnd::ProviderIface:
+  CFX_Matrix GetWindowMatrix(CPWL_Wnd::PrivateData* pAttached) override;
 
   virtual void GetActionData(CPDFSDK_PageView* pPageView,
                              CPDF_AAction::AActionType type,
diff --git a/fpdfsdk/formfiller/cffl_interactiveformfiller.cpp b/fpdfsdk/formfiller/cffl_interactiveformfiller.cpp
index 10cefd2..425c2ad 100644
--- a/fpdfsdk/formfiller/cffl_interactiveformfiller.cpp
+++ b/fpdfsdk/formfiller/cffl_interactiveformfiller.cpp
@@ -544,14 +544,15 @@
   m_Maps.erase(it);
 }
 
-void CFFL_InteractiveFormFiller::QueryWherePopup(void* pPrivateData,
-                                                 float fPopupMin,
-                                                 float fPopupMax,
-                                                 bool* bBottom,
-                                                 float* fPopupRet) {
-  CFFL_PrivateData* pData = reinterpret_cast<CFFL_PrivateData*>(pPrivateData);
+void CFFL_InteractiveFormFiller::QueryWherePopup(
+    CPWL_Wnd::PrivateData* pAttached,
+    float fPopupMin,
+    float fPopupMax,
+    bool* bBottom,
+    float* fPopupRet) {
+  auto* pData = static_cast<CFFL_PrivateData*>(pAttached);
   CPDFSDK_Widget* pWidget = pData->pWidget;
-  auto* pPage = pWidget->GetPDFPage();
+  CPDF_Page* pPage = pWidget->GetPDFPage();
 
   CFX_FloatRect rcPageView(0, pPage->GetPageHeight(), pPage->GetPageWidth(), 0);
   rcPageView.Normalize();
@@ -767,9 +768,10 @@
   return true;
 }
 
-bool CFFL_InteractiveFormFiller::OnPopupPreOpen(void* pPrivateData,
-                                                uint32_t nFlag) {
-  CFFL_PrivateData* pData = reinterpret_cast<CFFL_PrivateData*>(pPrivateData);
+bool CFFL_InteractiveFormFiller::OnPopupPreOpen(
+    CPWL_Wnd::PrivateData* pAttached,
+    uint32_t nFlag) {
+  auto* pData = static_cast<CFFL_PrivateData*>(pAttached);
   ASSERT(pData);
   ASSERT(pData->pWidget);
 
@@ -777,9 +779,10 @@
   return OnPreOpen(&pObserved, pData->pPageView, nFlag) || !pObserved;
 }
 
-bool CFFL_InteractiveFormFiller::OnPopupPostOpen(void* pPrivateData,
-                                                 uint32_t nFlag) {
-  CFFL_PrivateData* pData = reinterpret_cast<CFFL_PrivateData*>(pPrivateData);
+bool CFFL_InteractiveFormFiller::OnPopupPostOpen(
+    CPWL_Wnd::PrivateData* pAttached,
+    uint32_t nFlag) {
+  auto* pData = static_cast<CFFL_PrivateData*>(pAttached);
   ASSERT(pData);
   ASSERT(pData->pWidget);
 
@@ -856,7 +859,7 @@
 }
 
 std::pair<bool, bool> CFFL_InteractiveFormFiller::OnBeforeKeyStroke(
-    void* pPrivateData,
+    CPWL_Wnd::PrivateData* pAttached,
     CFX_WideString& strChange,
     const CFX_WideString& strChangeEx,
     int nSelStart,
@@ -864,8 +867,7 @@
     bool bKeyDown,
     uint32_t nFlag) {
   // Copy the private data since the window owning it may not survive.
-  CFFL_PrivateData privateData =
-      *reinterpret_cast<CFFL_PrivateData*>(pPrivateData);
+  CFFL_PrivateData privateData = *static_cast<CFFL_PrivateData*>(pAttached);
   ASSERT(privateData.pWidget);
 
   CFFL_FormFiller* pFormFiller = GetFormFiller(privateData.pWidget, false);
@@ -921,7 +923,7 @@
         privateData.pPageView, nValueAge == privateData.pWidget->GetValueAge());
     if (!pWnd)
       return {true, true};
-    privateData = *reinterpret_cast<CFFL_PrivateData*>(pWnd->GetAttachedData());
+    privateData = *static_cast<CFFL_PrivateData*>(pWnd->GetAttachedData());
     bExit = true;
   }
   if (fa.bRC) {
diff --git a/fpdfsdk/formfiller/cffl_interactiveformfiller.h b/fpdfsdk/formfiller/cffl_interactiveformfiller.h
index b71f3a6..ddab2ad 100644
--- a/fpdfsdk/formfiller/cffl_interactiveformfiller.h
+++ b/fpdfsdk/formfiller/cffl_interactiveformfiller.h
@@ -126,13 +126,13 @@
       std::map<CPDFSDK_Annot*, std::unique_ptr<CFFL_FormFiller>>;
 
   // IPWL_Filler_Notify:
-  void QueryWherePopup(void* pPrivateData,
+  void QueryWherePopup(CPWL_Wnd::PrivateData* pAttached,
                        float fPopupMin,
                        float fPopupMax,
                        bool* bBottom,
                        float* fPopupRet) override;
   // Returns {bRC, bExit}.
-  std::pair<bool, bool> OnBeforeKeyStroke(void* pPrivateData,
+  std::pair<bool, bool> OnBeforeKeyStroke(CPWL_Wnd::PrivateData* pAttached,
                                           CFX_WideString& strChange,
                                           const CFX_WideString& strChangeEx,
                                           int nSelStart,
@@ -140,8 +140,10 @@
                                           bool bKeyDown,
                                           uint32_t nFlag) override;
 #ifdef PDF_ENABLE_XFA
-  bool OnPopupPreOpen(void* pPrivateData, uint32_t nFlag) override;
-  bool OnPopupPostOpen(void* pPrivateData, uint32_t nFlag) override;
+  bool OnPopupPreOpen(CPWL_Wnd::PrivateData* pAttached,
+                      uint32_t nFlag) override;
+  bool OnPopupPostOpen(CPWL_Wnd::PrivateData* pAttached,
+                       uint32_t nFlag) override;
   void SetFocusAnnotTab(CPDFSDK_Annot* pWidget, bool bSameField, bool bNext);
 #endif  // PDF_ENABLE_XFA
   void UnRegisterFormFiller(CPDFSDK_Annot* pAnnot);
@@ -151,7 +153,7 @@
   bool m_bNotifying;
 };
 
-class CFFL_PrivateData {
+class CFFL_PrivateData : public CPWL_Wnd::PrivateData {
  public:
   CPDFSDK_Widget* pWidget;
   CPDFSDK_PageView* pPageView;
diff --git a/fpdfsdk/formfiller/cffl_textfield.h b/fpdfsdk/formfiller/cffl_textfield.h
index 6893516..2a99413 100644
--- a/fpdfsdk/formfiller/cffl_textfield.h
+++ b/fpdfsdk/formfiller/cffl_textfield.h
@@ -24,7 +24,8 @@
   CFX_WideString sValue;
 };
 
-class CFFL_TextField : public CFFL_TextObject, public IPWL_FocusHandler {
+class CFFL_TextField : public CFFL_TextObject,
+                       public CPWL_Wnd::FocusHandlerIface {
  public:
   CFFL_TextField(CPDFSDK_FormFillEnvironment* pApp, CPDFSDK_Widget* pWidget);
   ~CFFL_TextField() override;
@@ -50,7 +51,7 @@
   bool IsFieldFull(CPDFSDK_PageView* pPageView) override;
 #endif
 
-  // IPWL_FocusHandler:
+  // CPWL_Wnd::FocusHandlerIface:
   void OnSetFocus(CPWL_Edit* pEdit) override;
 
  private:
diff --git a/fpdfsdk/pwl/cpwl_edit.cpp b/fpdfsdk/pwl/cpwl_edit.cpp
index 4558e43..8fbafd0 100644
--- a/fpdfsdk/pwl/cpwl_edit.cpp
+++ b/fpdfsdk/pwl/cpwl_edit.cpp
@@ -333,7 +333,7 @@
 void CPWL_Edit::OnSetFocus() {
   SetEditCaret(true);
   if (!IsReadOnly()) {
-    if (IPWL_FocusHandler* pFocusHandler = GetFocusHandler())
+    if (CPWL_Wnd::FocusHandlerIface* pFocusHandler = GetFocusHandler())
       pFocusHandler->OnSetFocus(this);
   }
   m_bFocus = true;
diff --git a/fpdfsdk/pwl/cpwl_edit.h b/fpdfsdk/pwl/cpwl_edit.h
index ef12e98..3e8de04 100644
--- a/fpdfsdk/pwl/cpwl_edit.h
+++ b/fpdfsdk/pwl/cpwl_edit.h
@@ -13,18 +13,20 @@
 #include "core/fxcrt/cfx_unowned_ptr.h"
 #include "fpdfsdk/pwl/cpwl_edit_ctrl.h"
 
+#define PWL_CLASSNAME_EDIT "CPWL_Edit"
+
 class IPWL_Filler_Notify {
  public:
   virtual ~IPWL_Filler_Notify() {}
 
   // Must write to |bBottom| and |fPopupRet|.
-  virtual void QueryWherePopup(void* pPrivateData,
+  virtual void QueryWherePopup(CPWL_Wnd::PrivateData* pAttached,
                                float fPopupMin,
                                float fPopupMax,
                                bool* bBottom,
                                float* fPopupRet) = 0;
   virtual std::pair<bool, bool> OnBeforeKeyStroke(
-      void* pPrivateData,
+      CPWL_Wnd::PrivateData* pAttached,
       CFX_WideString& strChange,
       const CFX_WideString& strChangeEx,
       int nSelStart,
@@ -32,8 +34,10 @@
       bool bKeyDown,
       uint32_t nFlag) = 0;
 #ifdef PDF_ENABLE_XFA
-  virtual bool OnPopupPreOpen(void* pPrivateData, uint32_t nFlag) = 0;
-  virtual bool OnPopupPostOpen(void* pPrivateData, uint32_t nFlag) = 0;
+  virtual bool OnPopupPreOpen(CPWL_Wnd::PrivateData* pAttached,
+                              uint32_t nFlag) = 0;
+  virtual bool OnPopupPostOpen(CPWL_Wnd::PrivateData* pAttached,
+                               uint32_t nFlag) = 0;
 #endif  // PDF_ENABLE_XFA
 };
 
diff --git a/fpdfsdk/pwl/cpwl_wnd.cpp b/fpdfsdk/pwl/cpwl_wnd.cpp
index e259d1f..401fed3 100644
--- a/fpdfsdk/pwl/cpwl_wnd.cpp
+++ b/fpdfsdk/pwl/cpwl_wnd.cpp
@@ -44,6 +44,8 @@
 
 CPWL_Wnd::CreateParams::CreateParams(const CreateParams& other) = default;
 
+CPWL_Wnd::CreateParams::~CreateParams() = default;
+
 class CPWL_MsgControl : public CFX_Observable<CPWL_MsgControl> {
   friend class CPWL_Wnd;
 
@@ -181,12 +183,12 @@
 
 void CPWL_Wnd::OnDestroy() {}
 
-void CPWL_Wnd::InvalidateFocusHandler(IPWL_FocusHandler* handler) {
+void CPWL_Wnd::InvalidateFocusHandler(FocusHandlerIface* handler) {
   if (m_CreationParams.pFocusHandler == handler)
     m_CreationParams.pFocusHandler = nullptr;
 }
 
-void CPWL_Wnd::InvalidateProvider(IPWL_Provider* provider) {
+void CPWL_Wnd::InvalidateProvider(ProviderIface* provider) {
   if (m_CreationParams.pProvider.Get() == provider)
     m_CreationParams.pProvider.Reset();
 }
@@ -482,8 +484,8 @@
   return m_CreationParams.sDash;
 }
 
-void* CPWL_Wnd::GetAttachedData() const {
-  return m_CreationParams.pAttachedData;
+CPWL_Wnd::PrivateData* CPWL_Wnd::GetAttachedData() const {
+  return m_CreationParams.pAttachedData.Get();
 }
 
 CPWL_ScrollBar* CPWL_Wnd::GetVScrollBar() const {
@@ -670,11 +672,11 @@
   return m_CreationParams.pSystemHandler;
 }
 
-IPWL_FocusHandler* CPWL_Wnd::GetFocusHandler() const {
-  return m_CreationParams.pFocusHandler;
+CPWL_Wnd::FocusHandlerIface* CPWL_Wnd::GetFocusHandler() const {
+  return m_CreationParams.pFocusHandler.Get();
 }
 
-IPWL_Provider* CPWL_Wnd::GetProvider() const {
+CPWL_Wnd::ProviderIface* CPWL_Wnd::GetProvider() const {
   return m_CreationParams.pProvider.Get();
 }
 
@@ -718,7 +720,7 @@
 
 CFX_Matrix CPWL_Wnd::GetWindowMatrix() const {
   CFX_Matrix mt = GetChildToRoot();
-  if (IPWL_Provider* pProvider = GetProvider())
+  if (ProviderIface* pProvider = GetProvider())
     mt.Concat(pProvider->GetWindowMatrix(GetAttachedData()));
   return mt;
 }
diff --git a/fpdfsdk/pwl/cpwl_wnd.h b/fpdfsdk/pwl/cpwl_wnd.h
index 4074e93..2fd5077 100644
--- a/fpdfsdk/pwl/cpwl_wnd.h
+++ b/fpdfsdk/pwl/cpwl_wnd.h
@@ -22,10 +22,8 @@
 class CPWL_Edit;
 class CPWL_MsgControl;
 class CPWL_ScrollBar;
-class CPWL_Wnd;
 class CFX_SystemHandler;
 class IPVT_FontMap;
-class IPWL_Provider;
 struct PWL_SCROLL_INFO;
 
 // window styles
@@ -65,8 +63,6 @@
 // combobox styles
 #define PCBS_ALLOWCUSTOMTEXT 0x0001L
 
-#define PWL_CLASSNAME_EDIT "CPWL_Edit"
-
 struct CPWL_Dash {
   CPWL_Dash() : nDash(0), nGap(0), nPhase(0) {}
   CPWL_Dash(int32_t dash, int32_t gap, int32_t phase)
@@ -104,47 +100,53 @@
 #define PWL_DEFAULT_BLACKCOLOR CFX_Color(COLORTYPE_GRAY, 0)
 #define PWL_DEFAULT_WHITECOLOR CFX_Color(COLORTYPE_GRAY, 1)
 
-class IPWL_Provider : public CFX_Observable<IPWL_Provider> {
- public:
-  virtual ~IPWL_Provider() {}
-
-  // get a matrix which map user space to CWnd client space
-  virtual CFX_Matrix GetWindowMatrix(void* pAttachedData) = 0;
-};
-
-class IPWL_FocusHandler {
- public:
-  virtual ~IPWL_FocusHandler() {}
-  virtual void OnSetFocus(CPWL_Edit* pEdit) = 0;
-};
-
 class CPWL_Wnd : public CPWL_TimerHandler, public CFX_Observable<CPWL_Wnd> {
  public:
-  struct CreateParams {
+  class PrivateData {
+   protected:
+    ~PrivateData() {}
+  };
+
+  class ProviderIface : public CFX_Observable<ProviderIface> {
+   public:
+    virtual ~ProviderIface() {}
+
+    // get a matrix which map user space to CWnd client space
+    virtual CFX_Matrix GetWindowMatrix(PrivateData* pAttached) = 0;
+  };
+
+  class FocusHandlerIface {
+   public:
+    virtual ~FocusHandlerIface() {}
+    virtual void OnSetFocus(CPWL_Edit* pEdit) = 0;
+  };
+
+  class CreateParams {
    public:
     CreateParams();
     CreateParams(const CreateParams& other);
+    ~CreateParams();
 
-    CFX_FloatRect rcRectWnd;                      // required
-    CFX_SystemHandler* pSystemHandler;            // required
-    IPVT_FontMap* pFontMap;                       // required
-    IPWL_Provider::ObservedPtr pProvider;         // required
-    IPWL_FocusHandler* pFocusHandler;             // optional
-    uint32_t dwFlags;                             // optional
-    CFX_Color sBackgroundColor;                   // optional
-    CPDFSDK_Widget::ObservedPtr pAttachedWidget;  // required
-    BorderStyle nBorderStyle;                     // optional
-    int32_t dwBorderWidth;                        // optional
-    CFX_Color sBorderColor;                       // optional
-    CFX_Color sTextColor;                         // optional
-    int32_t nTransparency;                        // optional
-    float fFontSize;                              // optional
-    CPWL_Dash sDash;                              // optional
-    void* pAttachedData;                          // optional
-    CPWL_Wnd* pParentWnd;                         // ignore
-    CPWL_MsgControl* pMsgControl;                 // ignore
-    int32_t eCursorType;                          // ignore
-    CFX_Matrix mtChild;                           // ignore
+    CFX_FloatRect rcRectWnd;                          // required
+    CFX_SystemHandler* pSystemHandler;                // required
+    IPVT_FontMap* pFontMap;                           // required
+    ProviderIface::ObservedPtr pProvider;             // required
+    CFX_UnownedPtr<FocusHandlerIface> pFocusHandler;  // optional
+    uint32_t dwFlags;                                 // optional
+    CFX_Color sBackgroundColor;                       // optional
+    CPDFSDK_Widget::ObservedPtr pAttachedWidget;      // required
+    BorderStyle nBorderStyle;                         // optional
+    int32_t dwBorderWidth;                            // optional
+    CFX_Color sBorderColor;                           // optional
+    CFX_Color sTextColor;                             // optional
+    int32_t nTransparency;                            // optional
+    float fFontSize;                                  // optional
+    CPWL_Dash sDash;                                  // optional
+    CFX_UnownedPtr<PrivateData> pAttachedData;        // optional
+    CPWL_Wnd* pParentWnd;                             // ignore
+    CPWL_MsgControl* pMsgControl;                     // ignore
+    int32_t eCursorType;                              // ignore
+    CFX_Matrix mtChild;                               // ignore
   };
 
   CPWL_Wnd();
@@ -182,8 +184,8 @@
   virtual CFX_FloatRect GetFocusRect() const;
   virtual CFX_FloatRect GetClientRect() const;
 
-  void InvalidateFocusHandler(IPWL_FocusHandler* handler);
-  void InvalidateProvider(IPWL_Provider* provider);
+  void InvalidateFocusHandler(FocusHandlerIface* handler);
+  void InvalidateProvider(ProviderIface* provider);
   void Create(const CreateParams& cp);
   void Destroy();
   void Move(const CFX_FloatRect& rcNew, bool bReset, bool bRefresh);
@@ -220,7 +222,7 @@
   const CFX_FloatRect& GetClipRect() const;
 
   CPWL_Wnd* GetParentWindow() const;
-  void* GetAttachedData() const;
+  PrivateData* GetAttachedData() const;
 
   bool WndHitTest(const CFX_PointF& point) const;
   bool ClientHitTest(const CFX_PointF& point) const;
@@ -234,8 +236,8 @@
   CPWL_ScrollBar* GetVScrollBar() const;
 
   IPVT_FontMap* GetFontMap() const;
-  IPWL_Provider* GetProvider() const;
-  IPWL_FocusHandler* GetFocusHandler() const;
+  ProviderIface* GetProvider() const;
+  FocusHandlerIface* GetFocusHandler() const;
 
   int32_t GetTransparency();
   void SetTransparency(int32_t nTransparency);