It has to be in PDF, which can be a bit tiresome if you don't want to have to pay for a licence.
There is a free trial link on the upload section, but that is, not surprisingly, time limited.
I've used this link which seems to be free "for ever",
https://www.freepdfconvert.com/ but it does limit you to one document (an hour) I think but if you've only got the odd document or two does well enough.