VS 2017 Stamping pdf backgrounds with the ability to specify pages

Hi

I work with pdfs of several thousand pages (letters) and have the need to stamp a pdf as background (letterhead graphics).

Easy enough if the backgrounds are all the same - but the snag is that I need to vary the pdf used as background and there can be 4 variants.

I had in mind taking a database which states which background is needed and looping through it - ie:

record 1 states background A, so put background A onto page 1 of the pdf
record 2 states background B, so put background B onto page 2 of the pdf

etc etc

From what I've googled so far I would have to create a new pdf after each stamp, which is unwieldy.

Does anyone know of a way to go through a pdf and stamp a different specified pdf as background for each page?

I'd be happy to use a 3rd part command line tool to do each individual stamp and control the data loop from vb if there is such a utility?

Any pointers on this would be most welcome!