How to sign a PDF

I am looking for the easiest way in your opinions to digitally sign a pdf file in order to verify the file integrity in C#. I have found this http://www.nitropdf.com/help/using_digital_signatures.htm but nothing that I can run using C#
But, let me explain my situation...I have the command prompt outputting some computer specific data to a text file, which I wish to upload to a file signing server to sign. I was thinking convert the text file to pdf, and sign, but can anyone think of a better way? thanks!

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