A QR code just links to a URL. If you link to a URL that you own or control, it'll be fine. The problem comes when people use a link shortener that allows the destination to be changed later, or if they lose control of the domain or its backend.

What does censoring the "or" in porn accomplish?

ive just heard of an incident where students redirected their books codes to p**n. can i make sure that doesnt happen?

This is kind of confusing, or at least leaves a lot of detail out 😆 Did the domain lapse? Did their short-URL account get hacked? In any case, your QR code will just be encoding a URL. Ultimately, any URL can be redirected by someone out there; so it's just a matter of trusting that whoever has that access won't act maliciously, and that malicious actors can't gain access.

also, im using google to generate them, is there a foss alternative as im scared of tracking.

There absolutely are, just search and you should find plenty. Again, though, the QR code is just encoding a URL. Does Google use their own short-URL service for their generated QR codes? Just scan the QR code and look at the URL it encodes. If it's only the URL you want - not some Google short-URL that then redirects to the URL you entered - then there can't be any tracking done on it by Google.

lastly, can i make the qr code redirect to a specific page of a pdf

Covered by another commenter already, but for completeness: yes, you just add #page={n) at the end of the URL, e.g. https://dagrs.berkeley.edu/sites/default/files/2020-01/sample.pdf#page=5

ive just heard of an incident where students redirected their books codes to p**n

Where did you hear about this? It sounds suspiciously like someone misremembered the following incident where there was no malice or even intent, just incompetence and happenstance:

Children's snack recalled after its website caught serving porn

No, its just a coded form of a URL. People just dont know this and use weird online generators / link grabbers. Sometimes these use URL shorteners too, where easy typos can happen

There is also a PC based offline barcode generator called Zint. I've used it a lot over the years. It can generate regular barcodes, QR codes, or other ones. It's very handy. You can generate using batch files with it also, if you have a lot to do.

Sure there are foss qr code generators, I don't know any at the moment but with a simple google search you should find what you want. About the pdf on a specific page, I think you can add #page={pageNumber} in the url and should open it at the given page.

as for foss generators, there's an app on f-droid called Binary Eye for reading and generating assorted bar codes, including qr codes.