When I used to send press releases I tried to cover my bases. I would send it attached in a .doc format, as nearly everyone has MS Office, Google docs or something that will open that format. In addition, I copy/pasted the text into the email just to be safe (and because, frankly, some people don’t bother opening attachments).
As far as sending, email and fax both work.
You want to make it as easy as possible for the recipient to get it. I’ve attached helpful articles for reference.
Best to you!