When double clicking a pdf attachment, Adobe Reader opens up the attachment as expected. However, when clicking on the pdf document just once, so you can view it using the QuickViewer, it will display the pdf on the client but the client will freeze right after.
If you have Acrobat Reader Version 11 installed on your workstation try installing Adobe Reader DC instead. The GroupWise client should work fine with Adobe Reader DC.
GroupWise appears to have problems using Adobe Reader Version 11. The DC versions cooperates better with the GroupWise client code.