PDFs or PDF's

What is the official general rule for this? PDF’s or PDFs?

What do you mean by “official”?

This is a question of style. You consult the style guide used for your publication. If you are not writing for a publication, you can decide your own style.

Personally, I prefer “PDFs.”

Chicago says only with a period or both capital and lower-case letters. MLA says no. APA says no.

I’m going to take a third option and say: PDF files.

I guess you missed the big fight about this raging in another thread. :smiley:

In general, omit punctuation if it doesn’t serve a purpose. The apostrophe in “PDF’s” doesn’t serve a purpose (eg making pronunciation clearer, as in “A’s and E’s” versus “As and Es”), so I’d always leave it out.

Edit: unless, of course, the context is “the PDF’s properties” or “the PDF’s on its way”, or something. :slight_smile:

In general, the apostrophe for plurals is being phased out. It only remains when the lack of it would cause confusion (e.g., “A’s” vs “As”).