I am able to view encrypted PDFs fine in Reader X.
Which platform are you testing?
Answers to the questions below may help in looking into the issue further:
1. Are you unable to view some specific PDFs or is it happening for all PDFs?
2. What is the exact encryption method/software you are using to encrypt the PDFs?
3. What is the error message you are getting?
4. You mentioned that the Digital IDs carried over from version 9. Did you have Acrobat 9 or Reader 9 prior to installing Reader X?
5. Which platform are you on?
Goto Edit>Protection>Security Settigs
Click the 'Digital IDs' on the left hand side of the dialog box. Do you see the Digital ID required by the PDF to open? If not you can import them by clicking 'Add ID' button. Relaunch the Adobe Reader and try opening the PDF again.
AKAIK, digital IDs are not automatically imported from Adobe Reader 9 into Adobe Reader X. You have add them all over again.
Announcement: Would you like to help us improve Adobe Reader?
We have had a few bug reports related to Adobe Reader X protected mode coming in from you in this forum. We have addressed a large number of them in our upcoming Reader update and we would like to hear your feedback.
To that extent, we would like to invite you to the Adobe Reader Prerelease program and try out the latest build. To participate, please fill in the form available at https://www.adobe.com/cfusion/mmform/index.cfm?name=reader_prerelease_ interest and indicate Adobe Reader as the product of your interest.
We look forward to your active participation, feedback and help towards making Reader a better product.
Thanks and regards,
Adobe Prerelease Team