Where is the conditional setting about grades?
Your site administrator needs to turn it on in Site administration > Advanced features > Enable conditional access.
My old watermark does not work
The default certificate type code sets the transparency of the watermark image to 10%. Either change the watermark image so it is darker or adjusts the $pdf_SetAlpha setting. See Certificate customizing and the “Adjusting transparency of an image” section.
Where can I download a copy of Certificate
You can download Certificate for LMS from the LMS plugins database.