Remove flattened fields from AcroForm [pdfium : main]
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Kuka (Gerrit)
Jun 3, 2026, 11:24:24 AM (yesterday) Jun 3
to pdfium-...@googlegroups.com
Kuka has uploaded the change for review![]( "Open in Gerrit")
Commit message
Remove flattened fields from AcroForm
Remove widget annotations from AcroForm fields when flattening a page, and keep fields that are still referenced by other pages.
Add coverage for shared annotation arrays and shared widget annotations across pages.
Bug: 498010830
Change-Id: I001c9780375eb297e40f5b1f87698ac9a6a47fe7
Change diff
diff --git a/fpdfsdk/fpdf_flatten.cpp b/fpdfsdk/fpdf_flatten.cpp
index eb89264..00ed3ae 100644
--- a/fpdfsdk/fpdf_flatten.cpp
+++ b/fpdfsdk/fpdf_flatten.cpp
@@ -9,6 +9,7 @@
#include <limits.h>
#include <algorithm>
+#include <set>
#include <sstream>
#include <utility>
#include <vector>
@@ -16,6 +17,7 @@
#include "constants/annotation_common.h"
#include "constants/annotation_flags.h"
#include "constants/font_encodings.h"
+#include "constants/form_fields.h"
#include "constants/page_object.h"
#include "core/fpdfapi/edit/cpdf_contentstream_write_utils.h"
#include "core/fpdfapi/page/cpdf_page.h"
@@ -30,6 +32,7 @@
#include "core/fpdfapi/parser/cpdf_stream_acc.h"
#include "core/fpdfapi/parser/fpdf_parser_utility.h"
#include "core/fpdfdoc/cpdf_annot.h"
+#include "core/fxcrt/containers/contains.h"
#include "core/fxcrt/fx_string_wrappers.h"
#include "fpdfsdk/cpdfsdk_helpers.h"
@@ -38,6 +41,12 @@
namespace {
+constexpr char kAcroForm[] = "AcroForm";
+constexpr char kAnnots[] = "Annots";
+constexpr char kFields[] = "Fields";
+constexpr char kXFA[] = "XFA";
+constexpr int kMaxRecursion = 32;
+
bool IsValidRect(const CFX_FloatRect& rect, const CFX_FloatRect& rcPage) {
static constexpr float kMinSize = 0.000001f;
if (rect.IsEmpty() || rect.Width() < kMinSize || rect.Height() < kMinSize) {
@@ -314,6 +323,125 @@
SanitizeFontResources(resources_dict->GetMutableDictFor("Font"));
}
+bool IsWidgetAnnot(const CPDF_Dictionary* annot) {
+ return annot && annot->GetNameFor(pdfium::annotation::kSubtype) == "Widget";
+}
+
+void CollectPageWidgetAnnots(const CPDF_Dictionary* page_dict,
+ std::set<const CPDF_Dictionary*>* widget_annots) {
+ RetainPtr<const CPDF_Array> annots = page_dict->GetArrayFor(kAnnots);
+ if (!annots) {
+ return;
+ }
+
+ for (size_t i = 0; i < annots->size(); ++i) {
+ RetainPtr<const CPDF_Dictionary> annot = annots->GetDictAt(i);
+ if (IsWidgetAnnot(annot.Get())) {
+ widget_annots->insert(annot.Get());
+ }
+ }
+}
+
+void RemoveWidgetsReferencedByOtherPages(
+ CPDF_Document* document,
+ const CPDF_Dictionary* current_page_dict,
+ std::set<const CPDF_Dictionary*>* widget_annots) {
+ for (int i = 0, page_count = document->GetPageCount();
+ i < page_count && !widget_annots->empty(); ++i) {
+ RetainPtr<const CPDF_Dictionary> page_dict = document->GetPageDictionary(i);
+ if (!page_dict || page_dict.Get() == current_page_dict) {
+ continue;
+ }
+
+ std::set<const CPDF_Dictionary*> other_page_widget_annots;
+ CollectPageWidgetAnnots(page_dict.Get(), &other_page_widget_annots);
+ for (const CPDF_Dictionary* annot : other_page_widget_annots) {
+ widget_annots->erase(annot);
+ }
+ }
+}
+
+bool PruneFieldArray(CPDF_Array* fields,
+ const std::set<const CPDF_Dictionary*>& widget_annots,
+ std::set<const CPDF_Dictionary*>* visited_fields,
+ int level);
+
+bool ShouldPruneField(CPDF_Dictionary* field,
+ const std::set<const CPDF_Dictionary*>& widget_annots,
+ std::set<const CPDF_Dictionary*>* visited_fields,
+ int level) {
+ if (level > kMaxRecursion) {
+ return false;
+ }
+
+ if (pdfium::Contains(widget_annots, field)) {
+ return true;
+ }
+
+ RetainPtr<CPDF_Array> kids =
+ field->GetMutableArrayFor(pdfium::form_fields::kKids);
+ if (!kids || !visited_fields->insert(field).second) {
+ return false;
+ }
+
+ return PruneFieldArray(kids.Get(), widget_annots, visited_fields,
+ level + 1) &&
+ kids->IsEmpty();
+}
+
+bool PruneFieldArray(CPDF_Array* fields,
+ const std::set<const CPDF_Dictionary*>& widget_annots,
+ std::set<const CPDF_Dictionary*>* visited_fields,
+ int level) {
+ bool pruned = false;
+ for (size_t i = fields->size(); i > 0; --i) {
+ const size_t field_index = i - 1;
+ RetainPtr<CPDF_Dictionary> field = fields->GetMutableDictAt(field_index);
+ if (field &&
+ ShouldPruneField(field.Get(), widget_annots, visited_fields, level)) {
+ fields->RemoveAt(field_index);
+ pruned = true;
+ }
+ }
+ return pruned;
+}
+
+void RemoveFlattenedFields(CPDF_Document* document,
+ const CPDF_Dictionary* page_dict,
+ int level) {
+ std::set<const CPDF_Dictionary*> widget_annots;
+ CollectPageWidgetAnnots(page_dict, &widget_annots);
+ if (widget_annots.empty()) {
+ return;
+ }
+
+ RemoveWidgetsReferencedByOtherPages(document, page_dict, &widget_annots);
+ if (widget_annots.empty()) {
+ return;
+ }
+
+ RetainPtr<CPDF_Dictionary> root = document->GetMutableRoot();
+ if (!root) {
+ return;
+ }
+
+ RetainPtr<CPDF_Dictionary> acro_form = root->GetMutableDictFor(kAcroForm);
+ if (!acro_form) {
+ return;
+ }
+
+ RetainPtr<CPDF_Array> fields = acro_form->GetMutableArrayFor(kFields);
+ if (!fields) {
+ return;
+ }
+
+ std::set<const CPDF_Dictionary*> visited_fields;
+ PruneFieldArray(fields.Get(), widget_annots, &visited_fields, level);
+ if (fields->IsEmpty() && !acro_form->KeyExist(kXFA)) {
+ root->RemoveFor(kAcroForm);
+ }
+}
+
} // namespace
FPDF_EXPORT int FPDF_CALLCONV FPDFPage_Flatten(FPDF_PAGE page, int nFlag) {
@@ -496,6 +624,7 @@
sFormName.c_str());
pNewXObject->SetDataAndRemoveFilter(sStream.unsigned_span());
}
- pPageDict->RemoveFor("Annots");
+ RemoveFlattenedFields(document, pPageDict.Get(), /*level=*/0);
+ pPageDict->RemoveFor(kAnnots);
return FLATTEN_SUCCESS;
}
diff --git a/fpdfsdk/fpdf_flatten_embeddertest.cpp b/fpdfsdk/fpdf_flatten_embeddertest.cpp
index ec1073f..e11a99b 100644
--- a/fpdfsdk/fpdf_flatten_embeddertest.cpp
+++ b/fpdfsdk/fpdf_flatten_embeddertest.cpp
@@ -134,6 +134,29 @@
EXPECT_TRUE(FPDF_SaveAsCopy(document(), this, 0));
ScopedSavedDoc saved_doc = OpenScopedSavedDocument();
ASSERT_TRUE(saved_doc);
- // TODO(crbug.com/498010830): this should be FORMTYPE_NONE
+ EXPECT_EQ(FORMTYPE_NONE, FPDF_GetFormType(saved_doc.get()));
+}
+
+TEST_F(FPDFFlattenEmbedderTest, FlattenSharedAnnotArrayKeepsAcroForm) {
+ ASSERT_TRUE(OpenDocument("bug_498010830_shared_annots.pdf"));
+ ScopedPage page = LoadScopedPage(0);
+ ASSERT_TRUE(page);
+ EXPECT_EQ(FPDFPage_Flatten(page.get(), FLAT_NORMALDISPLAY), FLATTEN_SUCCESS);
+
+ EXPECT_TRUE(FPDF_SaveAsCopy(document(), this, 0));
+ ScopedSavedDoc saved_doc = OpenScopedSavedDocument();
+ ASSERT_TRUE(saved_doc);
+ EXPECT_EQ(FORMTYPE_ACRO_FORM, FPDF_GetFormType(saved_doc.get()));
+}
+
+TEST_F(FPDFFlattenEmbedderTest, FlattenSharedWidgetAnnotKeepsAcroForm) {
+ ASSERT_TRUE(OpenDocument("bug_498010830_shared_widget.pdf"));
+ ScopedPage page = LoadScopedPage(0);
+ ASSERT_TRUE(page);
+ EXPECT_EQ(FPDFPage_Flatten(page.get(), FLAT_NORMALDISPLAY), FLATTEN_SUCCESS);
+
+ EXPECT_TRUE(FPDF_SaveAsCopy(document(), this, 0));
+ ScopedSavedDoc saved_doc = OpenScopedSavedDocument();
+ ASSERT_TRUE(saved_doc);
EXPECT_EQ(FORMTYPE_ACRO_FORM, FPDF_GetFormType(saved_doc.get()));
}
diff --git a/testing/resources/bug_498010830_shared_annots.in b/testing/resources/bug_498010830_shared_annots.in
new file mode 100644
index 0000000..88bab06
--- /dev/null
+++ b/testing/resources/bug_498010830_shared_annots.in
@@ -0,0 +1,43 @@
+{{header}}
+{{object 1 0}}
+<<
+ /Type /Catalog
+ /Pages 2 0 R
+ /AcroForm << /Fields [ 6 0 R ] >>
+>>
+endobj
+{{object 2 0}}
+<< /Count 2 /Kids [ 3 0 R 4 0 R ] /Type /Pages >>
+endobj
+{{object 3 0}}
+<<
+ /Type /Page
+ /Parent 2 0 R
+ /MediaBox [ 0 0 300 300 ]
+ /Annots 5 0 R
+>>
+endobj
+{{object 4 0}}
+<<
+ /Type /Page
+ /Parent 2 0 R
+ /MediaBox [ 0 0 300 300 ]
+ /Annots 5 0 R
+>>
+endobj
+{{object 5 0}}
+[ 6 0 R ]
+endobj
+{{object 6 0}}
+<<
+ /Type /Annot
+ /FT /Tx
+ /T (Shared Annot Array Widget)
+ /Rect [ 100 100 200 130 ]
+ /Subtype /Widget
+>>
+endobj
+{{xref}}
+{{trailer}}
+{{startxref}}
+%%EOF
diff --git a/testing/resources/bug_498010830_shared_annots.pdf b/testing/resources/bug_498010830_shared_annots.pdf
new file mode 100644
index 0000000..c42010a
--- /dev/null
+++ b/testing/resources/bug_498010830_shared_annots.pdf
@@ -0,0 +1,56 @@
+%PDF-1.7
+% ò¤ô
+1 0 obj
+<<
+ /Type /Catalog
+ /Pages 2 0 R
+ /AcroForm << /Fields [ 6 0 R ] >>
+>>
+endobj
+2 0 obj
+<< /Count 2 /Kids [ 3 0 R 4 0 R ] /Type /Pages >>
+endobj
+3 0 obj
+<<
+ /Type /Page
+ /Parent 2 0 R
+ /MediaBox [ 0 0 300 300 ]
+ /Annots 5 0 R
+>>
+endobj
+4 0 obj
+<<
+ /Type /Page
+ /Parent 2 0 R
+ /MediaBox [ 0 0 300 300 ]
+ /Annots 5 0 R
+>>
+endobj
+5 0 obj
+[ 6 0 R ]
+endobj
+6 0 obj
+<<
+ /Type /Annot
+ /FT /Tx
+ /T (Shared Annot Array Widget)
+ /Rect [ 100 100 200 130 ]
+ /Subtype /Widget
+>>
+endobj
+xref
+0 7
+0000000000 65535 f
+0000000015 00000 n
+0000000104 00000 n
+0000000169 00000 n
+0000000264 00000 n
+0000000359 00000 n
+0000000384 00000 n
+trailer <<
+ /Root 1 0 R
+ /Size 7
+>>
+startxref
+510
+%%EOF
diff --git a/testing/resources/bug_498010830_shared_widget.in b/testing/resources/bug_498010830_shared_widget.in
new file mode 100644
index 0000000..4c32bcc
--- /dev/null
+++ b/testing/resources/bug_498010830_shared_widget.in
@@ -0,0 +1,40 @@
+{{header}}
+{{object 1 0}}
+<<
+ /Type /Catalog
+ /Pages 2 0 R
+ /AcroForm << /Fields [ 5 0 R ] >>
+>>
+endobj
+{{object 2 0}}
+<< /Count 2 /Kids [ 3 0 R 4 0 R ] /Type /Pages >>
+endobj
+{{object 3 0}}
+<<
+ /Type /Page
+ /Parent 2 0 R
+ /MediaBox [ 0 0 300 300 ]
+ /Annots [ 5 0 R ]
+>>
+endobj
+{{object 4 0}}
+<<
+ /Type /Page
+ /Parent 2 0 R
+ /MediaBox [ 0 0 300 300 ]
+ /Annots [ 5 0 R ]
+>>
+endobj
+{{object 5 0}}
+<<
+ /Type /Annot
+ /FT /Tx
+ /T (Shared Widget)
+ /Rect [ 100 100 200 130 ]
+ /Subtype /Widget
+>>
+endobj
+{{xref}}
+{{trailer}}
+{{startxref}}
+%%EOF
diff --git a/testing/resources/bug_498010830_shared_widget.pdf b/testing/resources/bug_498010830_shared_widget.pdf
new file mode 100644
index 0000000..6a17075
--- /dev/null
+++ b/testing/resources/bug_498010830_shared_widget.pdf
@@ -0,0 +1,52 @@
+%PDF-1.7
+% ò¤ô
+1 0 obj
+<<
+ /Type /Catalog
+ /Pages 2 0 R
+ /AcroForm << /Fields [ 5 0 R ] >>
+>>
+endobj
+2 0 obj
+<< /Count 2 /Kids [ 3 0 R 4 0 R ] /Type /Pages >>
+endobj
+3 0 obj
+<<
+ /Type /Page
+ /Parent 2 0 R
+ /MediaBox [ 0 0 300 300 ]
+ /Annots [ 5 0 R ]
+>>
+endobj
+4 0 obj
+<<
+ /Type /Page
+ /Parent 2 0 R
+ /MediaBox [ 0 0 300 300 ]
+ /Annots [ 5 0 R ]
+>>
+endobj
+5 0 obj
+<<
+ /Type /Annot
+ /FT /Tx
+ /T (Shared Widget)
+ /Rect [ 100 100 200 130 ]
+ /Subtype /Widget
+>>
+endobj
+xref
+0 6
+0000000000 65535 f
+0000000015 00000 n
+0000000104 00000 n
+0000000169 00000 n
+0000000268 00000 n
+0000000367 00000 n
+trailer <<
+ /Root 1 0 R
+ /Size 6
+>>
+startxref
+481
+%%EOF
Change information
Files:
- M fpdfsdk/fpdf_flatten.cpp
- M fpdfsdk/fpdf_flatten_embeddertest.cpp
- A testing/resources/bug_498010830_shared_annots.in
- A testing/resources/bug_498010830_shared_annots.pdf
- A testing/resources/bug_498010830_shared_widget.in
- A testing/resources/bug_498010830_shared_widget.pdf
Change size: L
Delta: 6 files changed, 345 insertions(+), 2 deletions(-)
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Lei Zhang (Gerrit)
Jun 3, 2026, 10:42:59 PM (18 hours ago) Jun 3
to Kuka, Lei Zhang, Tom Sepez, pdfium-...@googlegroups.com
Attention needed from Kuka and Tom Sepez
Lei Zhang added 6 comments![]( "Open in Gerrit")
Commit Message
Line 9, Patchset 3 (Latest):
Remove widget annotations from AcroForm fields when flattening a page, and keep fields that are still referenced by other pages.Lei Zhang . unresolved
Please wrap at 72 columns.
File fpdfsdk/fpdf_flatten.cpp
Line 331, Patchset 3 (Latest):
std::set<const CPDF_Dictionary*>* widget_annots) {Lei Zhang . unresolved
Just return this, instead of using an out-parameter.
Line 345, Patchset 3 (Latest):
void RemoveWidgetsReferencedByOtherPages(Lei Zhang . unresolved
It wasn't obvious if this is removing the widgets from a dictionary, or from the set. Since this is a set operation, how about "RemoveSharedWidgetsFromSet"?
Line 359, Patchset 3 (Latest):
widget_annots->erase(annot);Lei Zhang . unresolved
Use std::set_difference() instead?
Line 369, Patchset 3 (Latest):
bool ShouldPruneField(CPDF_Dictionary* field,Lei Zhang . unresolved
Intuitive, this name sounds like it is trying to answer a question, so it should be logically const. But it is not. Is there a way to do the decision making, and then prune?
File testing/resources/bug_498010830_shared_annots.in
Line 3, Patchset 3 (Latest):
<<Lei Zhang . unresolved
Please use testing/resources/344775293.in as an example and format the .in file in the same manner. Then regenerate the .pdf.
Related details
Attention is currently required from:
- Kuka
- Tom Sepez
Submit Requirements:
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Kuka (Gerrit)
11:57 AM (4 hours ago) 11:57 AM
to Lei Zhang, Tom Sepez, pdfium-...@googlegroups.com
Attention needed from Lei Zhang and Tom Sepez
Kuka added 7 comments![]( "Open in Gerrit")
Patchset-level comments
File-level comment, Patchset 8 (Latest):
Kuka . unresolved
Thanks for the review. I addressed the comments and uploaded a new patch set.
Could you please take another look when you have time?
Commit Message
Line 9, Patchset 3:
Remove widget annotations from AcroForm fields when flattening a page, and keep fields that are still referenced by other pages.Lei Zhang . resolved
Please wrap at 72 columns.
Kuka
Done
File fpdfsdk/fpdf_flatten.cpp
Just return this, instead of using an out-parameter.
Kuka
Done
It wasn't obvious if this is removing the widgets from a dictionary, or from the set. Since this is a set operation, how about "RemoveSharedWidgetsFromSet"?
Kuka
Done. Renamed it to RemoveSharedWidgetsFromSet().
Line 359, Patchset 3:
widget_annots->erase(annot);Lei Zhang . resolved
KukaUse std::set_difference() instead?
Done
Intuitive, this name sounds like it is trying to answer a question, so it should be logically const. But it is not. Is there a way to do the decision making, and then prune?
Kuka
Done. I split the decision from the pruning side effect. The old
ShouldPruneField() helper is gone now. PruneFieldArray() first decides whether
the current field should be removed, and only then removes it from the array.
File testing/resources/bug_498010830_shared_annots.in
Please use testing/resources/344775293.in as an example and format the .in file in the same manner. Then regenerate the .pdf.
Attention is currently required from:
- Lei Zhang
- Tom Sepez
Submit Requirements:
Code-Owners
Code-Review
No-Unresolved-Comments
Review-Enforcement
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