I recently starting writing a scan to pdf document storage application for use in house. It works slick, documents are scanned using sane and scanbuttond triggers it. TIFF and pdf documents are push to the web as single pages where they can be printed, downloaded and e-mailed. But I need a simple way to merge the pdf documents into multipage documents. TIFF tools has a solution, tiffcp.
Usage:
tiffcp image1.tiff image2.tiff image3.tiff merged.tiff
Then converting to pdf is as simple as:
tiff2pdf merged.tiff -o merged.pdf