You can select “Page Range” under the “Pages to Stamp” section in the stamp dialog.
Choose a start page and an end page.   A page number of -1 can be used to specify the last page of the file.  Use the “Increment” box to set an incremental number of pages to be stamped.  Setting the value to 1 will stamp every page, 2 will stamp ever second page, 5 will stamp every fifth page and so on. 

If you need additional ways to select pages, look at our desktop product – StampPDF DE.