extracting letters from a PDF based on page naming

[djbats]

A client supplies a single PDF containing three letters, (a two page letter, a three page letter and a five page letter). The pages in the PDF are named 1,2,1,2,3,1,2,3,4,5. Is there a way to extract these three letters automatically so that each pdf contains a single letter starting at page 1? this would be to run a script adding white text to the headers of each first page as required by our mailroom software. Or is there a script that can add white text to pages named "1" and not just the first page of a pdf? Hope this makes sense to someone.

[djbats]

..or is it possible I could run a script to add a background form to pages containing a specific string of words? this would enable me to add white text to relevant pages only, hope this makes sense too.