Most legitimate third-party sites list the password directly on the download page, often near the download link or in a "README" section.
Open the archive in WinRAR and look at the right-hand panel. Uploaders often put the password in the "Archive Comment" section. Warning: The "Password.txt" Trap skidrow games winrar password
These are almost always scams designed to generate revenue for the uploader or infect your computer with adware. Most legitimate third-party sites list the password directly