To set your default projection across all of ArcPad, you can take a .prj file and rename it to ArcPad.prj and place it in your "My ArcPad" folder on your device. This is for version 10, I think if you are working with an earlier version you would put the ArcPad.prj file in the "My Documents" folder.
To set your default projection across all of ArcPad, you can take a .prj file and rename it to ArcPad.prj and place it in your "My ArcPad" folder on your device. This is for version 10, I think if you are working with an earlier version you would put the ArcPad.prj file in the "My Documents" folder.