I have configured free fax for asterisk and it's works properly.
But the tif/pdf file is often wrong (incomplete or unreadable), and often I receive only one page of all transmitted pages.
In this situation, I can't use asterisk to receive fax because It's not reliable.
I use free fax with Digium TDM400P and asterisk version is: Asterisk 126.96.36.199.1
Please let me know if you need more details.