Overlay 2 pdf files to be one file

Hello, I have two seperate 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 each page overlaying on each one.

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

I hope its clear.

I have acrabat pro dc.

Thanks