Sorry, when the user gets deleted you can not retrieve their PDF. What you are looking for is https://github.com/mdjnelson/moodle-mod_customcert/issues/38 but it requires a developer and a lot of time.
Thanks, Mark for your return. Good to know it exists a possibility 
I have another request:
From a course that has SCORM files, and that participants already completed them, I added a certificate, with the completion date to be displayed (that might have happened before adding the certificate). When I test, logging in from a participant profile, to download the certificate, the date doesn't appear.
Could you explain to me why?
Thanks!
I have another request:
From a course that has SCORM files, and that participants already completed them, I added a certificate, with the completion date to be displayed (that might have happened before adding the certificate). When I test, logging in from a participant profile, to download the certificate, the date doesn't appear.
Could you explain to me why?
Thanks!
Are you running cron on your site (https://docs.moodle.org/310/en/Cron)?