For the rare case where the file is benign (e.g., a legitimate archive from a trusted forum like RuBoard*, though still illegal), the password is often one of:

Legitimate software developers do not password-protect their installers without providing the password immediately. If you download a trial from Adobe, it works. If you buy it, the license key unlocks it. So, why do pirates password-protect ZIP files?

If you’ve already downloaded a ZIP and are desperately searching for the password, stop. Instead, scan the file with (without extracting). If the detection rate is above 3–5 engines, delete the file immediately.