The original post was asking "Must you be able to show an auditor that you own a copy of ISO9001". Several posts so far have correctly pointed out the answer to this as "absolutely not".
Other posts have touched on the subject of copyright issues - do copies of the standard have to be original, purchased copies?
I have to say that under UK (and I suspect other countries') copyright law, you are definitely NOT permitted to buy one copy, then photocopy it as many times as you like. It doesn't matter if you have an original copy somewhere.
There are some relaxations of this - e.g. you can make temporary copies for training purposes, but these have to be withdrawn and destroyed. You can also lend the document within your organisation, but as soon as you make a copy you are breaking the law. This applies to electronic downloads as well as hard copy versions.
Our BSI auditor occasionally asks to see that all of our copies are originals (we purchased 10 copies for our internal auditors), and I have put a sticker on each identifying it to an Excel database that logs who has it, etc.
I'm also reasonably sure that if he were to see an illegal copy, he is obliged to report it. Especially since he works for the company that stand to lose $$$ through illegal copying of standards. I'm certain that our guy would raise it.
Randy and others are right to say it is not a big issue, but I did hear several years ago about a major computer manufacturer who were fined a large amount when an auditor discovered ONE photocopy of ISO9001. The fine was based not on how many illegal copies were actually found, but how many copies a company of that size would be expected to have, given that copyright was shown to have been infringed.
These stories are few and far between, which suggests no-one cares that much - but SOMEONE will get caught next.