I will use Let’s Encrypt and JupyterHub. I got domain-key.txt, domain-crt.txt, domain-csr.txt and account-key.txt.
I found an article at Stackoverflow. The created files from Let’s Encrypt uses base64, which is readable in ASCII, not binary format: The certificates is allredy in PEM format. Just change the extension to *.pem.
For JupyterHub I need a privkey.pem and fullchain.pem. I copied domain-key.txt to privkey.pem and doamin-crt.txt to fullchain.pem.
Due to the file names I suppose you got your certificate using zerossl website, if that is correct then yes, domain-key.txt is privkey.pem and domain-crt.txt is fullchain.pem because the last one includes your cert and the Let’s Encrypt Intermediate cert.
Keep in mind that Let’s Encrypt certificates are only valid for 90 days so you should repeat this manual process once every 90 days (or every 60 days just to be sure there is no problem and you have at least 30 more days to fix the issue before your certificate expires).