Im not a developer so can't help with writing code. However, i do have an alternative. I believe both Windows and OS X have the ability to print screen to PDF when you hit CRTL + P or CMD + P. If this is just for you, this may be sufficient. If this is for any teacher in your Moodle instance, then this may be too much because you will need to write instructions on how to do so.
Another similiar alternative is researching the various add-ons and extensions available for the browser you use. I have heard of some that allow you to print your screen to PDF.
Gradebook
Export to PDF
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