The Laserfiche repository itself does not have the concept of password protection for files. Some file formats - pdf and zip most commonly - do support password protection, and users can place these documents in the repository. When users attempt to view the contents, they may be prompted to enter a password by the viewing application (winzip, or in this case the javascript-based pdf renderer) - but note that these credentials don't leave the viewing application. That is to say, the Laserfiche system does not know and has never known the password for this file.

Unfortunately for you, the pdf encryption scheme is fairly robust, and there's no easy way to circumvent it. The weakest link is usually the user's choice of password, but you would probably need an automated guesser to have a chance.