ADE is unable (on PC-eReaders) to open password protected files and it was created to manage only DRM protected and "fully non protected" epub-pdf files, you must go to other app in your eReader able to manage traditional pdf files, perhaps this app is included in the app pool of your eReader. Another approach is removing password from your pdf. You must be sure than password protected PDF are not the more secure files.
Unfortunately, this won't work - because the password protection can be set
by the publisher and cannot be changed by the user. Also, if the file is
encrypted, it cannot be managed by ADE - which is the way ADE was designed,
as noted above. That's not true of Adobe Reader, which is based on your
computer, not your ereader. So, it's not possible to download an encrypted
file to your ereader and open it with ADE. That does NOT mean that your
ereader won't work with encrypted files IF you use a different software.
I'm not sure of all the software out there, so I can't suggest a particular
one, but a little Google work might do the trick.
Sorry!
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