Using MBS FileMaker Plugin and our DynaPDF functions, you can process a report generated by FileMaker and put a letter paper behind each page. Our example database (in next prerelease) shows you how to do this.
You can use two PDFs for letter paper, one for first page and second one for other pages. The letter paper PDFs can be stored in container fields or files on disk. You can have either one PDF for both pages or two PDFs, one for each page. Your script can even dynamically switch for each report to use different PDFs depending on the company branch, customer language or other criteria.
The only important thing is to have the report draw no background in the PDF which would hide the underlaying letter paper content. Of course we could add more plugin functions to remove unwanted background from a PDF for such a processing.
(The watermark goes away if you purchase a license of the DynaPDF Pro library and our plugin.)