Brother MFC-3420C - Manual (Page 91)

USING THE WINDOWS ® XP-BASED BROTHER SMARTUI CONTROL CENTER 4 - 15
Scan to File
The Scan to File button allows you to scan an image and save it in
a specific file type to any directory on your hard disk. This allows you
to easily archive your paper original s. To configure the file type and
save to directory right-click on the Scan to File button and click
Configuration.
The Scan Action tab is set to File and should not be changed.