How can I force the A4 format of incoming fax messages?

Incoming fax message are delivered as a PDF, but the PDF does not have the correct A4 format. How can I force that?

In the XPhone Server web interface under SETTINGS -> UM -> FAX -> GENERAL in the "Advanced Settings" set a new parameter called Fax2Mail\Tiff2Pdf with the value ForceA4

Save the parameter and then the main page itself. Now the UM services should be marked for a restart. Start the UM services.