[gettalong]

I don't think LetsEncrypt provides such a service. Additionally, the certificate must/should come from a CA that is included in the AATL (https://helpx.adobe.com/acrobat/kb/approved-trust-list1.html), otherwise you won't get the nice visual check mark that the signature is okay on Adobe Reader (and, let's face it, this is what most people are probably gonna be using on Windows).

Agreed on cumbersome, I have a PNG file with transparency containing my signature and use Xournal++ (https://xournalpp.github.io/) for placing it on the PDFs. That works fine but still takes more time than I want to spend. But it's faster than typing it out every time.