I’m assuming you’re concerned with resume manipulation? Or is there another reason you prefer to submit your resume in a non-editable format?
But I'm guessing that's your point, right? Because the hiring manager should notice, and the interview process should screen for it, so this must be a symptom of much larger scale dysfunction in the tech recruiting/hiring space.
"You mean FOOlang? Yeah, a little."
"And what jobs did you have when you did that?"
"Uh, I learned a little about FOOlang in the job I had from 2010-2012, and then it came up again in the job in 2015."
"Thanks! I think I'll have something for you tomorrow."
And then the recruiter edits "Skills" to include six years of the still-misheard FOOLAND.
Everything else is worse.
Oh yes. As the candidate this is also great when the interviewer says something like “It says here you’ve worked with x” and you go “I’m fairly certain that that wasn’t on there when I submitted the resume (to the recruiter), let me see that” and it turns out like the OP said, extra skill added in a different font.
"It says on your resume you have extensive experience in X."
"I do not."
They also have a thing for stripping your name and contact details out and pasting their ugly letterhead over the top. Which I suppose they could still do with a PDF if they have Acrobat Pro.
This makes some amount of sense because they want to avoid the company bypassing the recruiter and their commission. I was once hired like this (although I didn't know it until much later, when the owner told me). I think it's a realistic and reasonable fear.
I have a "redacted" version of my CV for this purpose which removes the personal information, but I can't recall I ever actually used it since I haven't really used recruiters for a decade.
They usually strip the content from it and drop it into a container resume that has their details so that they get credit from the hire I assume. lol. That being said, whatever the poster was doing to stop the resume from being edited is moot. They will just copy the content from the PDF and paste it into a new one.