Simple app to fill data into the pdf template https://www.codeguru.com/csharp/.net/net_general/generating-a-pdf-document-using-c-.net-and-itext-7.html add signature/image to existing pdf: PdfReader reader = new PdfReader ( pdfIn ) FileStream fs = new FileStream ( pdfOut , FileMode . Create ); var stamper = new PdfStamper ( reader , fs ); var pdfContentByte = stamper . GetOverContent ( 1 ); iTextSharp . text . Image sigimage = iTextSharp . text . Image . GetInstance ( bytes ); sigimage . SetAbsolutePosition ( 100 , 100 ); pdfContentByte . AddImage ( sigimage ); Create Google cloud functions https://codelabs.developers.google.com/codelabs/cloud-functions-csharp/index.html?index=..%2F..index#0