Ricoh Gestetner DSm790 Operating Instructions Manual page 140

Copying
A
Press [Stamp].
2
B
Press [Page Nmbr.].
C
Select the format.
You can specify the stamp, position, pages to be stamped, and numbering.
D
After you specify all desired settings, press [OK].
E
Place the originals, and then press the {Start} key.
Reference
"Stamp", General Settings Guide
120