Tiny, strange numbers in corners of PDFs?

[Avatar Name Redacted by User]

Hi, I noticed that there were strange numbers in the corners of all my Paizo PDFs, which are normally too small to see unless you zoom in really, really far.

The numbers seem to be the same on each PDF, and advance by one in each page. For example, the number in the upper left corner of the title page is 910500, the number in the upper left in page 2 is 910501, etc. Why are these here?

[Leg o' Lamb]

Anti-piracy is my guess.

[David knott 242]

I thought the watermark at the bottom of the page served that purpose, but maybe this is additional protection. Still, the way the number varies suggests that it could simply be a combination of product number and page number.

[Avatar Name Redacted by User]

It's the same numbers on each PDF, albeit limited by the number of pages.

Does anyone else have the numbers on their PDFs? And if so, is the top left number on the title page the same as mine or different?

(If this is an anti-piracy feature, I'm actually quite annoyed that Paizo also uses obtrusive watermarks when this serves the exact same purpose without being obtrusive.)

[Cori Marie]

It looks to be something that is only on Second Edition books for me, as my first edition books don't seem to have them. The number is the same on all of my second edition books, regardless of book or type of book even.

[David knott 242]

I am not finding it. Which PDF(s) should I look at?

[Leg o' Lamb]

It’s on every pdf. I noticed this several years ago. Find one with a dark cover; zoom in on a corner. There should be a series of numbers in white.