[Louis]

That should not happen.
Uploaders can assign pws for certain files, but of course they should be written in the post.
Some uploaders also try to cheat you by only giving you the pw when you first buy premium. You better report these guys to us.

In your case maybe try contacting the poster via personal message or check the rest of the thread to see if the pw is hidden somewhere else.

Maybe others can help if you post the link here.