Am I allowed to upload a recommendation letter directly into an admissions portal?

One of my mentors sent me a pdf of a recommendation letter he wrote. I already submitted my application on common app, would I be allowed to upload this directly into an applicant portal or would it be frowned upon? (Meaning I would have to ask him to email the school directly)

If it is through the common app, then there is supposed to be a link sent by the common app to your mentor (when you were supposed to invite recommenders) that leads to where he is supposed to fill out information.

The college will not accept any recommendations that have been in your hands.