To create a PDF version of a GLS label, you must add a NUL printer to Server Printers.
 

1. Go to Setup in nShift On-premises.
   
   
2. Select Installation, at the top level in the tree structure.
   
   
3. Open Server Printers and click New.
   
   
   
   
4. Choose an A4 or file printer, e.g. Microsoft Print to PDF, and click OK.
   
   
   
   
5. Select the printer, rename it to NUL, and make a short description. Set the type to Windows (label).
   
   
   
   
6. Click OK to save. You can now both save GLS labels as well as send them as attachments in e-mails using On-premises. 
   
   
7. Change the printer to the new printer on return shipments in the Production view to avoid getting the error "Label not found on database". Go to File > Print setup and choose the new printer.
   
   
   
   
8. Click OK to save.

Recommended reading: Sending return labels by email (Mailback).