FPDF_Creator can only create file through embedder-supplied callback.

core/include/fxcrt/fx_basic.h

Index: core/include/fxcrt/fx_basic.h
diff --git a/core/include/fxcrt/fx_basic.h b/core/include/fxcrt/fx_basic.h
index 7181b199427ce6ffbaa4a9edf2acc8f3c0460286..73b99be54962193f7c7d183df5ba07b27bac1fb0 100644
--- a/core/include/fxcrt/fx_basic.h
+++ b/core/include/fxcrt/fx_basic.h
@@ -164,18 +164,12 @@ class CFX_FileBufferArchive : public IFX_BufferArchive {
   ~CFX_FileBufferArchive() override;
 
   void Clear() override;
-
   FX_BOOL AttachFile(IFX_StreamWrite* pFile, FX_BOOL bTakeover = FALSE);
 
-  FX_BOOL AttachFile(const FX_WCHAR* filename);
-
-  FX_BOOL AttachFile(const FX_CHAR* filename);
-
  private:
   FX_BOOL DoWork(const void* pBuf, size_t size) override;
 
   IFX_StreamWrite* m_pFile;
-
   FX_BOOL m_bTakeover;
 };