@uk1000 has given you a great answer. As a fellow writer / proofreader I would recommend that you specify a default option in your gig description - MS Word is the obvious one to go with due to its universal take up and compatibility.
Take it form me, as a seller who’s been with Fiverr for a few years now, you absolutely need to nail the basics (such as file delivery format) in your gig description. Not to do so is opening yourself up to all sorts of complaints caused by assumptions on the part of the buyer.
Personally, I would suggest that opting for pdf is actually a poor choice. There’ll be some users who won’t know how to copy and paste the content into an editable format, thus causing them frustration and placing the blame on you. The only real world benefit of a pdf is that the document can’t easily be changed - which is likely to be the opposite of what most buyers want.
To take the above thought a step further, quite a few months back there was a poll on here about the most popular text / writing delivery formats. I can’t recall the exact result, but MS Word / docx format came out at about 98%. Although I use Apple Pages to write with, I always deliver the end result as a MS Word file.