The syntax of the print command is:
$host.print( BOOLEAN param1, INTEGER param2, INTEGER param3, BOOLEAN param4,
BOOLEAN param5, BOOLEAN param6, BOOLEAN param7, BOOLEAN param8 )
You need to change parameter 2 to the zero based start page number as a string, parameter 3 to the zero based page number as a string, and parameter 7 to 1 to use the values of parameter 2 and 3.
So if you have a 25 page PDF and you want a button to print pages 4 and 5 you would change the default code to:
print(0, 3, 4, 0, 0, 0, 1, 0)
More information is contained in the "Scripting Reference" under LiveCycle Designer's "Help" menu.