need to remove Acro X security on multiple files, purge index, build new index

You can't - it has to be done manually on each file.

Assuming the password is the same for all of the files, you can remove security with a batch sequence as explained here: http://blogs.adobe.com/acrobatforlifesciences/2010/04/removing_security_from_pdfs_in/

The details are important, so be sure to read through it carefully.

Unfortunately, George's solution is from an earlier version of Acrobat. Acrobat X Pro has totally nuked all the old batch processing in favor of its Action Wizard, which seems to have deleted much of the functionality of the old versions and made it impossible to do anything with any kind of efficiency. I really don't understand the mindset of making software less and less user-friendly with each new version.

I just tested this with Acrobat 10.1 and it worked fine. The only step in the process is "Encrypt" with the option of "Security Method: None" and "Start with: Ask When Action is Started". Be sure to change the user preference that is mentioned.

When run, it prompts with "Please enter password to open files" (note the inaccuracy) and saves the unsecured documents in a new location.

Hmm. Now I'm really confused. The document at the URL George gives above isn't the same as what we have, and we definitely have Acrobat X Pro. I tried to find the exact version, but couldn't find the details of exactly what version of X we have when I looked in Properties for the program. Maybe the URL was for an earlier version and there's a more current document?

The tutorial is indeed for Acrobat 9, but you should be able to set the same thing up with Acrobat 10. You just need to set up an new Action as I minimally described. If you get stuck, post again and include information about what you've tried.

I'm getting closer now. I did set up the action as described and have it set to None but it's not taking the security off. I'll have to play with it some more tomorrow. I'll post back with the specific steps I've done and see if I can get it to work. Maybe a fresh start tomorrow will clear things up!

I've always found the key to removing security on a folders of PDFs (assuming the password is the same for all the files)is to make sure the preference under Edit > Preferences > Action Wizard category is set to Password Security under the Security Method dropdown. This will make sure that you are prompted for the existing password on the files so they can be opened during execution of the Action to allow removal of the existing security.

Eureka! Thank you, Lori--that fixed it. For others' reference, here are the steps to set up the Action Wizard to remove security from a folder of files:
1. Go to Edit > Preferences > Action Wizard, set to Password Security under the Security Method dropdown.
2. In Acrobat, with no specific document open, go to Tools panel at top right, choose Action Wizard.
3. Choose Create New Action.
4. Open the Protection tab at the left, choose Encrypt.
5. At "Start with:" choose Ask when action is started.
6. At "Steps:" on Encrypt, choose Options, make sure Security Method is set to None.
7. At "Save to:" choose Ask when Action is Started.
8. Click Save button.
9. Name the action (I named it Remove Security).
And just to finish my original post, after I removed the security, I just deleted the old index and its folder from the previous time and did a new index build and it seemed to work just fine.
Thank you, George and Lori!

I have found that is best to keep an archive set of files without any security being applied. This allows for easy updating and modification. When need to distribute a protected version then make a copy of the files for distribution and use an batch process or action to apply needed security.