Overlay 2 pdf files into one

I have two separate pdf files, each 50 pages. I want to overlay one file on top of the other one, with the output being a single pdf document of 50 pages, with the content of the two pdfs overlayed page-wise.

I don't want the same page of document 2 as the background of document 1, but each page should merge. i.e page one of pdf 1 merge with page one of pdf 2, page two of pdf 1 merge with page two of pdf 2, etc.

I have found some expensive software that will do it, but I only have this one thing to do. Is there any freeware out there that can do this?

1 Answer

This is already nicely answered in stackoverflow:

You can do this with pdf files using the command line tool pdftk using the stamp or background option.

$ pdftk file1.pdf background file2.pdf output combinedfile.pdf

This will only work with a one-page background file. If you have multiple pages, you can use the multibackground command instead.