pdfGetDocumentFileSize

Size in bytes of the output file on disk. Meaningful after pdfCloseFile; before close (or for in-memory output) the file is missing or incomplete and the call returns 0/the bytes written so far. For in-memory documents use the BufSize from pdfGetBuffer instead.

int32_t __stdcall pdfGetDocumentFileSize(PPDF IPDF);

C# (P/Invoke)

public static extern int pdfGetDocumentFileSize(IntPtr IPDF);