If Master PDF Editor (MPE) is not listed all you need is to create a MasterPdfEditor.desktop file. Just press Ctrl+Alt+T on your keyboard to open Terminal. When it opens, run the command(s) below:
gksudo gedit /usr/share/applications/MasterPdfEditor.desktop
Copy and paste the following, and then save and close the file. (Note that the *.desktop files should be in /usr/share/applications).
Name=Master PDF Editor
Comment=PDF and XPS files editor
Categories=PDF Editor;XPS Editor;Office;Utility;Text Editor;
Right click on the PDF file --> Open With --> Open With Other Application
If you don't see Master PDF Editor in the list, click on Show Other Applications
Scroll down to Master PDF Editor, highlight it, and click on Use as Default.