XReader Document Viewer - Printing A4 document onto A4 paper

When I use XReader Document Viewer (the default PDF viewer on Fedora) to print an A4 page onto A4 paper, the page is always shrunk.
It is as though, for some reason, it shrinks the page to Letter size - although everything that I can see says 'A4'.
I checked this by

1. Printing a page of a document from Open Office Writer
2. Creating a PDF document of the same document
3. Printing the same page from XReader

The printed PDF was noticeably smaller than the original.
Any ideas what might cause this?

It also applies to other documents, not produced by me using Open Office.