This is only a scanner. To Fax, you will need a separate fax machine or fax modem. If both the scanner and fax machine are connected to your computer, you will be able to scan the document and then fax it from the computer. (Depending on your OS/software, this could be easy or take several steps. For Windows Vista and Windows 7, you can use Windows Fax and Scan to do both steps. (However, the program doesn't scan to PDFs.) Paperport will also send a scanned document to an installed fax option. PaperPort is part of the third-party software that came on the CD with the scanner.)
Documentation for the Visioneer OneTouch 8900 is available here: http://support.visioneer.com/products/8900/default.asp
I hope this helps.
(There are some email-to-fax and web-to-fax options but I have not reviewed them.)