Fix incremental PDF save functionality for edited documents Previously, CPDF_Creator::InitNewObjNumOffsets() would skip all objects in incremental save mode due to the condition: `if (is_incremental_ || pair.second->GetObjNum() == CPDF_Object::kInvalidObjNum)` This caused incremental saves to only contain metadata without actual content modifications, making the feature effectively broken. Changes: - Modified InitNewObjNumOffsets() to properly handle incremental mode - In incremental mode: include modified/new objects in new_obj_num_array_ - In non-incremental mode: preserve original logic (skip existing objects) - Updated SaveSimpleDocIncremental test expectation (985u -> 1178u bytes) - Added comprehensive test IncrementalSaveWithModifications to verify: * Modified objects are included in incremental saves * Saved documents render correctly with modifications * File structure contains proper incremental save markers The fix enables proper incremental saving of PDF documents after editing. Bug: 42270523 Change-Id: Ic055c78ac94991b5b147f4320447089e159ae67a Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/135350 Reviewed-by: Tom Sepez <tsepez@chromium.org> Commit-Queue: Tom Sepez <tsepez@chromium.org> Reviewed-by: Lei Zhang <thestig@chromium.org>

diff --git a/AUTHORS b/AUTHORS
index 4a65f36..612fdbc 100644
--- a/AUTHORS
+++ b/AUTHORS

@@ -40,6 +40,7 @@
 Peter Varga <pvarga@inf.u-szeged.hu>
 Ralf Sippl <ralf.sippl@gmail.com>
 Robert Collyer <rcollyer99@gmail.com>
+Rulong Chen（陈汝龙） <rulong.crl@alibaba-inc.com>
 Ryan Wiley <wileyrr@gmail.com>
 Satvic Dhawan <satvicdhawan14@gmail.com>
 Stefan Ziegler <sz5000@gmx.de>

diff --git a/core/fpdfapi/edit/cpdf_creator.cpp b/core/fpdfapi/edit/cpdf_creator.cpp
index deb2181..9d16ee3 100644
--- a/core/fpdfapi/edit/cpdf_creator.cpp
+++ b/core/fpdfapi/edit/cpdf_creator.cpp

@@ -218,11 +218,11 @@
 void CPDF_Creator::InitNewObjNumOffsets() {
   for (const auto& pair : *document_) {
     const uint32_t objnum = pair.first;
-    if (is_incremental_ ||
-        pair.second->GetObjNum() == CPDF_Object::kInvalidObjNum) {
+    if (pair.second->GetObjNum() == CPDF_Object::kInvalidObjNum) {
       continue;
     }
-    if (parser_ && parser_->IsValidObjectNumber(objnum) &&
+
+    if (!is_incremental_ && parser_ && parser_->IsValidObjectNumber(objnum) &&
         !parser_->IsObjectFree(objnum)) {
       continue;
     }

diff --git a/fpdfsdk/fpdf_save_embeddertest.cpp b/fpdfsdk/fpdf_save_embeddertest.cpp
index ac8ec4b..ae44648 100644
--- a/fpdfsdk/fpdf_save_embeddertest.cpp
+++ b/fpdfsdk/fpdf_save_embeddertest.cpp

@@ -13,6 +13,7 @@
 #include "public/fpdfview.h"
 #include "testing/embedder_test.h"
 #include "testing/embedder_test_constants.h"
+#include "testing/fx_string_testhelpers.h"
 #include "testing/gmock/include/gmock/gmock-matchers.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ -56,7 +57,8 @@
   // Version gets taken as-is from input document.
   EXPECT_THAT(GetString(), StartsWith("%PDF-1.7\n%\xa0\xf2\xa4\xf4"));
   // Additional output produced vs. non incremental.
-  EXPECT_EQ(985u, GetString().size());
+  // Check that the size is larger than the old, broken incremental save size.
+  EXPECT_GT(GetString().size(), 985u);
 }
 
 TEST_F(FPDFSaveEmbedderTest, SaveSimpleDocNoIncremental) {
@@ -224,3 +226,77 @@
   EXPECT_TRUE(FPDF_SaveAsCopy(document(), this, 0));
   EXPECT_THAT(GetString(), HasSubstr("/Foo/"));
 }
+
+TEST_F(FPDFSaveEmbedderTest, IncrementalSaveWithModifications) {
+  ASSERT_TRUE(OpenDocument("rectangles.pdf"));
+
+  ScopedPage page = LoadScopedPage(0);
+  ASSERT_TRUE(page);
+
+  // Get the original bitmap for comparison
+  ScopedFPDFBitmap original_bitmap = RenderLoadedPage(page.get());
+  std::string original_md5 = HashBitmap(original_bitmap.get());
+
+  // Count text objects on a page
+  auto count_text_objects = [](FPDF_PAGE page) {
+    int object_count = FPDFPage_CountObjects(page);
+    int text_count = 0;
+    for (int i = 0; i < object_count; ++i) {
+      FPDF_PAGEOBJECT obj = FPDFPage_GetObject(page, i);
+      if (FPDFPageObj_GetType(obj) == FPDF_PAGEOBJ_TEXT) {
+        ++text_count;
+      }
+    }
+    return text_count;
+  };
+
+  // Verify the original PDF does not have any text objects
+  EXPECT_EQ(0, count_text_objects(page.get()));
+
+  // Add a new text object to modify the page.
+  ScopedFPDFPageObject text_object(FPDFPageObj_NewTextObj(
+      document(), "Arial", 12.0f));
+  ScopedFPDFWideString text = GetFPDFWideString(L"Test Incremental Save");
+  FPDFText_SetText(text_object.get(), text.get());
+  FPDFPageObj_Transform(text_object.get(), 1, 0, 0, 1, 100, 100);
+  FPDFPage_InsertObject(page.get(), text_object.release());
+  ASSERT_TRUE(FPDFPage_GenerateContent(page.get()));
+
+  ASSERT_TRUE(FPDF_SaveAsCopy(document(), this, FPDF_INCREMENTAL));
+
+  // Verify the saved document
+  // Count occurrences of key markers
+  auto count_occurrences = [](const std::string& str, const std::string& substr) {
+    size_t count = 0;
+    size_t pos = 0;
+    while ((pos = str.find(substr, pos)) != std::string::npos) {
+      ++count;
+      pos += substr.size();
+    }
+    return count;
+  };
+
+  // Should contain incremental save markers (original + incremental)
+  std::string saved_content = GetString();
+  EXPECT_EQ(2u, count_occurrences(saved_content, "trailer"));
+  // In incremental PDF saving, /Prev points to the previous xref table's offset.
+  // Since we're doing only one incremental save operation, there's only one
+  // /Prev entry pointing to the original PDF's xref table.
+  EXPECT_EQ(1u, count_occurrences(saved_content, "/Prev"));
+  EXPECT_EQ(2u, count_occurrences(saved_content, "startxref"));
+  EXPECT_EQ(2u, count_occurrences(saved_content, "%%EOF"));
+
+  // Load the saved document and verify the modification is visible
+  ScopedSavedDoc saved_doc = OpenScopedSavedDocument();
+  ASSERT_TRUE(saved_doc);
+  ScopedSavedPage saved_page = LoadScopedSavedPage(0);
+  ASSERT_TRUE(saved_page);
+
+  // The rendered output should be different from the original
+  ScopedFPDFBitmap saved_bitmap = RenderSavedPage(saved_page.get());
+  std::string saved_md5 = HashBitmap(saved_bitmap.get());
+  EXPECT_NE(original_md5, saved_md5);
+
+  // Verify the text object exists after the save
+  EXPECT_EQ(1, count_text_objects(saved_page.get()));
+}