diff --git a/core/fpdfapi/page/cpdf_contentparser.cpp b/core/fpdfapi/page/cpdf_contentparser.cpp
index bd7c10f..eb99020 100644
--- a/core/fpdfapi/page/cpdf_contentparser.cpp
+++ b/core/fpdfapi/page/cpdf_contentparser.cpp
@@ -138,7 +138,7 @@
   DCHECK(m_pObjectHolder->IsPage());
   CPDF_Array* pContent =
       m_pObjectHolder->GetDict()->GetArrayFor(pdfium::page_object::kContents);
-  CPDF_Stream* pStreamObj = ToStream(
+  const CPDF_Stream* pStreamObj = ToStream(
       pContent ? pContent->GetDirectObjectAt(m_CurrentOffset) : nullptr);
   m_StreamArray[m_CurrentOffset] =
       pdfium::MakeRetain<CPDF_StreamAcc>(pStreamObj);
diff --git a/core/fpdfapi/page/cpdf_streamcontentparser.cpp b/core/fpdfapi/page/cpdf_streamcontentparser.cpp
index 02cee34..d407bc1 100644
--- a/core/fpdfapi/page/cpdf_streamcontentparser.cpp
+++ b/core/fpdfapi/page/cpdf_streamcontentparser.cpp
@@ -1295,7 +1295,7 @@
   size_t iSegment = 0;
   float fInitKerning = 0;
   for (size_t i = 0; i < n; i++) {
-    CPDF_Object* pObj = pArray->GetDirectObjectAt(i);
+    const CPDF_Object* pObj = pArray->GetDirectObjectAt(i);
     if (!pObj)
       continue;
 
diff --git a/core/fpdfapi/parser/cpdf_object_unittest.cpp b/core/fpdfapi/parser/cpdf_object_unittest.cpp
index fc11067..b42a7dd 100644
--- a/core/fpdfapi/parser/cpdf_object_unittest.cpp
+++ b/core/fpdfapi/parser/cpdf_object_unittest.cpp
@@ -829,8 +829,8 @@
   auto array = pdfium::MakeRetain<CPDF_Array>();
   CPDF_Object* pObj = array->AppendNew<CPDF_Number>(42);
   array->ConvertToIndirectObjectAt(0, &objects_holder);
-  CPDF_Object* pRef = array->GetObjectAt(0);
-  CPDF_Object* pNum = array->GetDirectObjectAt(0);
+  const CPDF_Object* pRef = array->GetObjectAt(0);
+  const CPDF_Object* pNum = array->GetDirectObjectAt(0);
   EXPECT_TRUE(pRef->IsReference());
   EXPECT_TRUE(pNum->IsNumber());
   EXPECT_NE(pObj, pRef);
diff --git a/core/fpdfdoc/cpdf_formfield.cpp b/core/fpdfdoc/cpdf_formfield.cpp
index 933cf5f..35449e2 100644
--- a/core/fpdfdoc/cpdf_formfield.cpp
+++ b/core/fpdfdoc/cpdf_formfield.cpp
@@ -73,10 +73,11 @@
 }
 
 // static
-WideString CPDF_FormField::GetFullNameForDict(CPDF_Dictionary* pFieldDict) {
+WideString CPDF_FormField::GetFullNameForDict(
+    const CPDF_Dictionary* pFieldDict) {
   WideString full_name;
-  std::set<CPDF_Dictionary*> visited;
-  CPDF_Dictionary* pLevel = pFieldDict;
+  std::set<const CPDF_Dictionary*> visited;
+  const CPDF_Dictionary* pLevel = pFieldDict;
   while (pLevel) {
     visited.insert(pLevel);
     WideString short_name = pLevel->GetUnicodeTextFor(pdfium::form_fields::kT);
diff --git a/core/fpdfdoc/cpdf_formfield.h b/core/fpdfdoc/cpdf_formfield.h
index 31665eb..1c7ddf1 100644
--- a/core/fpdfdoc/cpdf_formfield.h
+++ b/core/fpdfdoc/cpdf_formfield.h
@@ -80,7 +80,7 @@
   static CPDF_Object* GetFieldAttr(CPDF_Dictionary* pFieldDict,
                                    const ByteString& name);
 
-  static WideString GetFullNameForDict(CPDF_Dictionary* pFieldDict);
+  static WideString GetFullNameForDict(const CPDF_Dictionary* pFieldDict);
 
   WideString GetFullName() const;
   Type GetType() const { return m_Type; }
diff --git a/core/fpdfdoc/cpdf_generateap.cpp b/core/fpdfdoc/cpdf_generateap.cpp
index 3a26bd5..21a17d2 100644
--- a/core/fpdfdoc/cpdf_generateap.cpp
+++ b/core/fpdfdoc/cpdf_generateap.cpp
@@ -1251,12 +1251,12 @@
           if (FXSYS_IsFloatSmaller(fy, rcBody.bottom))
             break;
 
-          if (CPDF_Object* pOpt = pOpts->GetDirectObjectAt(i)) {
+          if (const CPDF_Object* pOpt = pOpts->GetDirectObjectAt(i)) {
             WideString swItem;
             if (pOpt->IsString()) {
               swItem = pOpt->GetUnicodeText();
-            } else if (CPDF_Array* pArray = pOpt->AsArray()) {
-              CPDF_Object* pDirectObj = pArray->GetDirectObjectAt(1);
+            } else if (const CPDF_Array* pArray = pOpt->AsArray()) {
+              const CPDF_Object* pDirectObj = pArray->GetDirectObjectAt(1);
               if (pDirectObj)
                 swItem = pDirectObj->GetUnicodeText();
             }
diff --git a/core/fpdfdoc/cpdf_interactiveform.cpp b/core/fpdfdoc/cpdf_interactiveform.cpp
index 98971e3..e111687 100644
--- a/core/fpdfdoc/cpdf_interactiveform.cpp
+++ b/core/fpdfdoc/cpdf_interactiveform.cpp
@@ -607,7 +607,7 @@
 }
 
 CPDF_FormField* CPDF_InteractiveForm::GetFieldByDict(
-    CPDF_Dictionary* pFieldDict) const {
+    const CPDF_Dictionary* pFieldDict) const {
   if (!pFieldDict)
     return nullptr;
 
@@ -670,7 +670,8 @@
   if (!pArray)
     return nullptr;
 
-  CPDF_Dictionary* pElement = ToDictionary(pArray->GetDirectObjectAt(index));
+  const CPDF_Dictionary* pElement =
+      ToDictionary(pArray->GetDirectObjectAt(index));
   return pElement ? GetFieldByDict(pElement) : nullptr;
 }
 
diff --git a/core/fpdfdoc/cpdf_interactiveform.h b/core/fpdfdoc/cpdf_interactiveform.h
index cca8770..178c054 100644
--- a/core/fpdfdoc/cpdf_interactiveform.h
+++ b/core/fpdfdoc/cpdf_interactiveform.h
@@ -58,7 +58,7 @@
 
   size_t CountFields(const WideString& csFieldName) const;
   CPDF_FormField* GetField(size_t index, const WideString& csFieldName) const;
-  CPDF_FormField* GetFieldByDict(CPDF_Dictionary* pFieldDict) const;
+  CPDF_FormField* GetFieldByDict(const CPDF_Dictionary* pFieldDict) const;
 
   const CPDF_FormControl* GetControlAtPoint(const CPDF_Page* pPage,
                                             const CFX_PointF& point,
diff --git a/fpdfsdk/cpdfsdk_interactiveform.cpp b/fpdfsdk/cpdfsdk_interactiveform.cpp
index 25dd6b9..1bddf19 100644
--- a/fpdfsdk/cpdfsdk_interactiveform.cpp
+++ b/fpdfsdk/cpdfsdk_interactiveform.cpp
@@ -190,7 +190,7 @@
       continue;
 
     for (size_t j = 0, jsz = pAnnots->size(); j < jsz; j++) {
-      CPDF_Object* pDict = pAnnots->GetDirectObjectAt(j);
+      const CPDF_Object* pDict = pAnnots->GetDirectObjectAt(j);
       if (pAnnotDict == pDict)
         return i;
     }