Use PDF Architect or Adobe Acrobat you open a PDF but you see "Please wait… If this message is not eventually replaced by the proper contents of the document, your PDF viewer may not be able to display this type of document." You know the PDF is good. You may or may not be prompted to enter a password to view the PDF. You don't think that the PDF viewer should be prompting you for a password.
Install Nitro Reader. Other PDF viewers may now be able to view the PDF.