Changing PDF paper types
Useful to know: use pdfinfo to find metadata and paper size, pdfjam to change the paper type/size specified in a PDF file.
pdfjam --outfile out.pdf --paper letter original_a4.pdf
As seen in Unix & Linux Stack Exchange http://unix.stackexchange.com/questions/185145/convert-pdf-to-a-different-page-size-us-letter-a4
[Source code formatting from http://codeformatter.blogspot.com/]