I assume you do not want to consume a license with you wanting to use the viewer. We don't use the viewer but force PADS into demo mode for viewing only stuff.
Put the below in a .bat file and run to make PADS run in demo mode.
start "" C:\MentorGraphics\PADSVX.2.3\SDD_HOME\common\win32\bin\powerpcb.exe
Thank you Wheels, works a treat.