What is the exact error message word-for-word? There's nothing illegal about making a backup copy of your own Office Disk and using the copy to install office (but unless you have a multiple copy license, you can only install it on one machine at a time - and it will allow you to activate it on only one machine at a time assuming it is a retail copy using the provided Product Key). If you obtained the ISO file from a company that downloads office files after paying for them (like the Microsoft Store) and then provides a product key, it's also fine to create a disk from that file (in fact, it's necessary if it's an ISO file).
If you downloaded the ISO file from some illegal or illegitimate site as a file or as a torrent (perhaps with a keygen to bypass the activation process) then you probably got a bad copy (most do not work properly), or maybe it is corrupt and/or infested with malware (which may have already severely infected your system), or perhaps it was detected as not merely a copy but an illegal copy and that's why it isn't working (and I most certainly will NEVER help you to bypass that security). In any event, if this is the case I do not want to know (as I will report it to the forum administrators) and I will offer you absolutely no assistance whatsoever in resolving this problem as it is illegal, unethical, and a serious violation of forum rules (and I personally find it extremely offensive).
Also, what version of Office is it (version and year)? And is it an upgrade copy or a full install copy and, if an upgrade copy, what version and year is currently installed? Is it a 32-bit or 64-bit version of Office (if an upgrade, what are both the old version and the new version)?