Steps:
  1. Right click PDF in Explorer, and open it with Xara Designer Pro X10.
  2. Edit PDF.
  3. Save it (Ctrl-s).
  4. Try to open it in Foxit Reader. I get: "Format Error: Not a PDF or corrupted."

With Xara the PDF can still be opened, possibly because it has been saved as a Xara file.

A workaround is exporting to PDF, but that's a bit cumbersome. Simply being able to save using Ctrl-s would be great. With JPEG images, for example, saving directly works fine.

I reported the bug to support.xara.com as ticket #QYJ-380-51374.