How to I protect my PDFs from being edited?

PDF protection is laughable. There's a quadrizillion tools and web sites out there that crack files in nanoseconds these days. Even if you add a password, it means nothing. So no, simply forget about it. Siomply convert the artwork or even rasterize it to pixel data and slap a big "Only for review" watermark on top, then hand out the final files only when everything has been agreed upon and it's finalized.

Mylenium

By the way - a rather newer feature in Acrobat DC (around 8 years ago) is automatic OCR. Allowing (comparatively) seamless editing of outlined or rasterised text. 

For items like logos and most other kinds of graphics I'll convert any live text to outlines in PDFs that I share with clients. I'll also password protect the PDF at the edit level. If I suspect a client is going to use my PDF sketches to get bids from rival companies I'll rasterize any of the vector artwork inside the PDF, giving the rivals nothing they can extract easily.

No, Adobe don't see this as a nifty NEW feature. Acrobat has had text editing for around 24 years now. I guess you just noticed.

Sorry. That's certainly not the answer you're hoping for.

But the only way to protect your PDF is not to share it.

All "protective measures" mean extra work and are more or less easy to circumvent, depending on your level of knowledge.

(Unless you convert the content of your PDF into a low quality pixel image. This makes editing much more difficult. But that is not actually the purpose of the PDF format.)

That is not possible.