FPDF_PageDelete must delete XFA pages as well.

fpdfsdk/fpdfeditpage.cpp

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include "public/fpdf_edit.h"
 
 #include "core/fpdfapi/fpdf_parser/include/cpdf_array.h"
 #include "core/fpdfapi/fpdf_parser/include/cpdf_document.h"
@@ skipping 39 matching lines @@
   if (pInfoDict) {
     if (FSDK_IsSandBoxPolicyEnabled(FPDF_POLICY_MACHINETIME_ACCESS))
       pInfoDict->SetAt("CreationDate", new CPDF_String(DateStr, FALSE));
     pInfoDict->SetAt("Creator", new CPDF_String(L"PDFium"));
   }
 
   return FPDFDocumentFromCPDFDocument(pDoc);
 }
 
 DLLEXPORT void STDCALL FPDFPage_Delete(FPDF_DOCUMENT document, int page_index) {
-  CPDF_Document* pDoc = CPDFDocumentFromFPDFDocument(document);
-  if (!pDoc || page_index < 0 || page_index >= pDoc->GetPageCount())
-    return;
-
-  pDoc->DeletePage(page_index);
+  if (UnderlyingDocumentType* pDoc = UnderlyingFromFPDFDocument(document))
+    pDoc->DeletePage(page_index);
 }
 
 DLLEXPORT FPDF_PAGE STDCALL FPDFPage_New(FPDF_DOCUMENT document,
                                          int page_index,
                                          double width,
                                          double height) {
   CPDF_Document* pDoc = CPDFDocumentFromFPDFDocument(document);
   if (!pDoc)
     return nullptr;
 
@@ skipping 233 matching lines @@
       !pPage->m_pFormDict->GetElement("Type")->GetDirect() ||
       pPage->m_pFormDict->GetElement("Type")->GetDirect()->GetString().Compare(
           "Page")) {
     return;
   }
   CPDF_Dictionary* pDict = pPage->m_pFormDict;
   rotate %= 4;
 
   pDict->SetAt("Rotate", new CPDF_Number(rotate * 90));
 }