Yes, you may add a paper copy of your transcript to your Interfolio account. If you have a paper copy of it in your possession, you may send that to Interfolio or you may have your registrar send the transcript directly to Interfolio. In both cases, you will need to generate a Request Form. The request form should be included with the transcript when it is mailed to Interfolio.
To add a transcript, click the "Add Document" link in your "My Documents" section, select "Transcript," in the "Document Type" and follow the on-screen instructions.
Please check with the eventual recipient of your transcript to make sure that a copy provided by Interfolio is acceptable. Many institutions will accept transcripts stored with Interfolio, but may request an original watermarked transcript that comes directly from the registrar of your institution at some point during the application process.
If you are applying to medical school, transcripts usually need to be sent directly to AMCAS and not to Interfolio.