podofo library creating bigger pdf file - podofo

Question

I am using podofo 0.9.3 library for digital signing pdf document using PdfSigIncMemDocument class. I am able to digitally sign pdf without any issue, but the output pdf file size is very big.
Here is my code
PdfSigIncMemDocument doc("e:\\sample.pdf");
char *buffer = NULL;
buffer = (char *)malloc(809600);
PdfOutputDevice output(buffer, 809600);
PdfSignOutputDevice signOutput(&output);
signOutput.SetSignatureSize(2048);
printf( "Page count:%d\n", doc.GetPageCount());
PdfSigIncSignatureField *sign = doc.GetSignatureField();
sign->SetSignatureDate(PdfDate());
sign->SetSignatureReason(L"I dont agree");
sign->SetSignatureImage("e:\\sign.jpg", 0, 100, 200, 100, 100);
sign->SetSignatureText(L"Hello World", 0, 100, 200, 100, 100, 12);
doc.Initialize();
doc.CreateVisualSign();
doc.Write(&signOutput);
printf( "Has Signature:%d\n", signOutput.HasSignaturePosition());
char buff[809600] = {0};
size_t len;
BYTE *Signature = NULL;
DWORD cbSignature = 0;
signOutput.AdjustByteRange();
signOutput.Seek(0);
len = signOutput.ReadForSignature(buff, 809600);
printf("total tbs size: %d\n", len);
SignMessage( (BYTE *)buff, len, &Signature, &cbSignature);//Digital signing using MSCAPI
printf("signature size: %d\n", cbSignature);
const PoDoFo::PdfData *sig = new PoDoFo::PdfData((char *)Signature, cbSignature);
signOutput.SetSignature(*sig);
signOutput.Flush();
FILE *fp = NULL;
fp = fopen( "e:\sign.pdf", "wb" );
fwrite( buffer, signOutput.GetLength(), 1, fp );
fclose(fp);
Size of sample.pdf is 31KB whereas the output sign.pdf size is 506KB.
can some one help with this issue ?