PDF stamping utility required

Hi all

I am looking for a utility that will stamp a reference into the margin of
each page of a PDF document. That reference is to be derived from the data
content within the stamped PDF document by an encrypted algorithm, so that
the reference uniquely identifies the document (well, perhaps not unique,
but a chance match being measured in the one in a million category).

I google and find a few utilities that will stamp watermarks onto pdf
documents but I cannot see any that advertise the extra step, ie that the
watermark is generated from the content of the document.

Any pointers gratefully received. Oh, and if it will run under Citrix, all
the better.

Thanks.

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