A legitimate ROM site will give you the file directly. If a site asks you to download a "special installer" to get the ROM, leave immediately.
Since direct links are often taken down, your best bet is to use trusted community archives. Look for these specific terms in your search engine: paper mario 64 z64 rom link
is the most common and preferred format. It represents a "big-endian" dump of the original cartridge, which is the native format for the Nintendo 64’s MIPS processor. A legitimate ROM site will give you the file directly
When searching for ROM links, keep these tips in mind to avoid malware: Look for these specific terms in your search
Downloading ROMs for games you do not physicaly own is technically a violation of copyright law. Always support official releases, such as the version available on the Nintendo Switch Online + Expansion Pack, whenever possible.