If you are running the 64 bit version of PDF Studio 8.3.1 or earlier on Ubuntu with the GTK or Nimbus look and feel, you might see extra space on the toolbars in PDF Studio.

There are two simple solutions to this:
1. Switch to the Metal or Substance look and feel
2. Upgrade to the latest version of PDF Studio, 8.3.2, Linux installer
Screenshot-PDF Studio Pro