Web service (C#) to digitally sign PDF documents

I just finished a bid from RentAcoder, the title is “Web service (C#) to digitally sign PDF documents”, it is a private bid, the requirement is,

Buyer needs a C# web service that will digitally sign a PDF created using ITextSharp.

The PDF will be already created and would be updated with a digital signature by the new web service. The web service would take as parameters the name of the document and some user authentication information (user id and password). The web service would validate the user id/password and sign the document digitally with a self-signed certificate.

The signature that appears on the document will be either an image of a signature or a unique text field like Sergie.Norwinski.123456.

The web service will also return a numeric return code and return message indicating success or failure.

The web service should also add the success or failure status to a SQL Server 2005 database. The database already contains the stored procedures to authenticate user identity and log the status of the request; the new web service simply needs to execute them.

Buyer will provide the self-signed certificates that are to be used by the web service.

And the buyer said,

Steven was an absolute delight to work with. He was very timely with his deliverables and the code provided worked as intended and was easily integrated into an existing application.

He was extremely flexible, accomodating, resourceful and has a great sense of ingenuity and creativity. Great C# skills and exceptional PDF and iTextSharp knowledge.

The pitfall of this bid, need parser PDF and get the x and y coordinates from the special given text, for example, get the x and y coordinates of “Signature/Credentials:” and put the signature after it, get the x and y coordinates of “Date Signed:”, and put the date string after it, but by default, iTextSharp does not support it.