Much of this goes to the heart of what the meaning of editor is.. I see it mostly an annotation, taking notes, highlighting, commnents on the PDF itself. The other person saw editing as changing the PDF itself.
For example, he had a PDF of a certificate and wanted to alter a line or two. While Master PDF Editor is certainly up to the job, this can be done rather simply within GIMP itself.
In this video I mainly use the Ink and Text tools to "extract text" and replace it with new text. An important note if you are a GIMP novice like myself is use layers liberally. Everytime you do a major action, create a new layer. This will make it much easier for you if you need to edit later on.