Introduce CPDF_Document::FromFPDFDocument().

fpdfsdk/src/fpdfeditpage.cpp

Index: fpdfsdk/src/fpdfeditpage.cpp
diff --git a/fpdfsdk/src/fpdfeditpage.cpp b/fpdfsdk/src/fpdfeditpage.cpp
index 8796d0e2b1a36465103800e25d1ff597abb60e53..574fa399c5f715b88ba9aa2c057ae2cb7f7adfd6 100644
--- a/fpdfsdk/src/fpdfeditpage.cpp
+++ b/fpdfsdk/src/fpdfeditpage.cpp
@@ -44,10 +44,8 @@ DLLEXPORT FPDF_DOCUMENT STDCALL FPDF_CreateNewDocument() {
 }
 
 DLLEXPORT void STDCALL FPDFPage_Delete(FPDF_DOCUMENT document, int page_index) {
-  CPDF_Document* pDoc = (CPDF_Document*)document;
-  if (pDoc == NULL)
-    return;
-  if (page_index < 0 || page_index >= pDoc->GetPageCount())
+  CPDF_Document* pDoc = CPDF_Document::FromFPDFDocument(document);
+  if (!pDoc || page_index < 0 || page_index >= pDoc->GetPageCount())
     return;
 
   pDoc->DeletePage(page_index);
@@ -57,17 +55,14 @@ DLLEXPORT FPDF_PAGE STDCALL FPDFPage_New(FPDF_DOCUMENT document,
                                          int page_index,
                                          double width,
                                          double height) {
-  if (!document)
-    return NULL;
+  CPDF_Document* pDoc = CPDF_Document::FromFPDFDocument(document);
+  if (!pDoc)
+    return nullptr;
 
-  //	CPDF_Parser* pParser = (CPDF_Parser*)document;
-  CPDF_Document* pDoc = (CPDF_Document*)document;
   if (page_index < 0)
     page_index = 0;
   if (pDoc->GetPageCount() < page_index)
     page_index = pDoc->GetPageCount();
-  //	if (page_index < 0 || page_index >= pDoc->GetPageCount())
-  //		return NULL;
 
   CPDF_Dictionary* pPageDict = pDoc->CreateNewPage(page_index);
   if (!pPageDict)