Authors have to scan the LoR and save it into PDF format and it must have their signatures. Digital signatures are not accepted, it should be a signature on the original paper letter then it's scanned.
Here's the AAMC's website instructions:
Uploading Your LoR
1. Applicants access MyERAS to enter and finalize LoR Authors.
2. Applicants print out the Letter Request Form for all LoR Authors and deliver it by email, mail, or in person.
Note: If an applicant waived his/her rights, they should not handle the completed letter.
3. LoR Authors complete their LoR; save it in PDF format; and access the LoRP to upload their letter.LoR Authors
4. LoR Authors and administrators register on the LoRP and create their username and password.
5. LoR Authors log in; enter the applicant's Letter ID; verify the applicant and LoR Author details; and follow the prompts to upload their letter in PDF format (PDFs with encryption, password protection, or digital signatures cannot be processed).
6. The LoR is transmitted to the ERAS PostOffice.
may view uploaded LoRs and/or upload new versions at any time (if needed). Once a LoR has been uploaded, it cannot be deleted or altered in any way. To make changes, you must submit a new version of the LoR. Programs will only be able to view the most recent LoR version.
Note: Using a central account, administrative users may repeat this process for each LoR/Letter ID combination that is provided to them.