How bad is it to print personal documents using an office printer? I would do it maybe once every six months, printing around 100 pages on average.
Regardless of the amount, using office equipment for personal stuff is 'not done' (formally/officially). I would not be surprised if that is written somewhere in your contract/agreements/company rules.
Just ask. Usually, for small amounts, companies don't see a problem and give you permission.
100 pages? What, are you printing a novel?
Every office I've worked in has turned a blind eye to the odd bit of personal printing. Paper confirmation for a ticket? Letter to the Tax Inspector? Sure, go ahead.
Ask your boss ahead of time, I can't imagine anyone caring about 1 or 2 pages.
But 100 pages? That's taking advantage of your company's good nature.
Honestly, a cheap laser printer is under £50 new. If you're going to be printing a lot, invest in one.
In my experience, printing a few things infrequently is fine - just like making infrequent, personal phone calls is fine and taking care of banking or something using your work computer is fine. 100 pages might be borderline, since that's enough that it can disrupt actual work for other people that need to print.
As long as you're getting your work done, not preventing others from getting their work done, and not using up hundreds of dollars of paper... it's usually fine.
It's not bad per se, many companies allow their employeed to print their personal stuff on the printer, such as tickets etc. When it's goint to the Master's thesis, it's in interest of the company to have worker higher qualified, at least usually. The costs are, be honest, minimal, so there's no really good reason for the company to forbid workers to print private stuff. It's really rare that the workers will have so much stuff to print that it would generate significant costs. It's often considered as a kind of benefit.
Of course, the company is free to forbid you doing so, and in that case, you must simply obey, no matter if you agree or not.
If you have any doubt on that matter, you should ask your management if it's OK or not.
I have seen people getting into issues because they printed personal documents. Usually printers are shared between offices and an employee from a different department will not be pleased to find out that they can't get their documents because someone is using the printer for personal purposes.
Talk to your supervisor and justify the cause. In case anything goes wrong, it is good to know that you talked to someone about it. I justify it by telling my manager how long it will take me to go to a local print shop and getting my documents.