When you make changes in the Userful Control Center, you must also Update your Presets. Otherwise any changes made, even after clicking Apply, will be lost the next time a scheduled Event is triggered.
Ensure Show only authenticated sessions is not checked in Usage Reports to see all data.
Add Master PDF to the dock.
If Master PDF does not appear in the list for you, contact Userful Support.
Downloading the PDF will save it to the desktop. From there it can be opened in Atril or Master PDF. If you want Master PDF to serve as the default viewer (over Atril), contact Userful Support.
This is unfortunately a known issue with CUPS (the printing back-end), and we are not able to resolve it. This behavior does not occur in LibreOffice.