This item is migrated to the Telerik Document Processing portal: http://feedback.telerik.com/Project/184/Feedback/Details/190101 Please use the new item for commenting, voting and subscribing instead of this one.
Looking around I found this: http://feedback.telerik.com/Project/154/Feedback/Details/153921-fix-radpdfviewer-some-secured-encrypted-pdf-files-are-not-decrypted-correctl and http://feedback.telerik.com/Project/154/Feedback/Details/153358-add-radpdfviewer-add-support-for-encryption-algorithm-4-exception-the-encryp Maybe cross-voting helps to speed up the development...
Well, to go further it would also be great to open and show secured documents. So you should vote for this also: http://feedback.telerik.com/Project/143/Feedback/Details/88622-crypt-filter.
I think the base for this would be this: http://feedback.telerik.com/Project/143/Feedback/Details/131525-support-encryption-aes-128-256bit-rc4-40-128bit-via-crypt-filter In a business environment AES is crucial. So please vote up the other item too.