I am not sure if the documents or files that you are opening or changing are from attachments sent to you via email or not, but I can suggest that you can try this step:
Right click on one of the affected files and select Get Info.
This will open a long narrow box providing detailed information of the document.
Now look at the bottom of the window under Sharing & Permissions
Click the padlock and enter your User Admin password when the pop up window appears.
This will allow you access to changing the current permissions of this document.
Make sure you see permissions for "Read and Write" attached to your user name.
If you do, then go ahead and close this window. However, if you see only Read permissions attached to your user, then change that to Read and Write.
Once you have done this, close this Get Info window.
Try to launch that affect document to see if it opens now. If it does then this may be a permissions issue that is affecting your documents and files.
Whether you can or not, I would still recommend you still run this procedure below in order to try and fix this permissions issue.
Now run Disk Utility to repair all permissions on your Mac OS X volume.
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-RUN DISK UTILITY-
Go to Finder Menu bar
• Click Go > Utilities >
Disk Utility and open up Disk Utility app.
• Click on Macintosh HD volume
(or on the name you have changed
• Select "Repair Disk Permissions"
**Let Disk Utilities run this
repair permissions until completion
Once Disk Utility is complete
and there are no errors in red in the completion summary (if there are errors
listed in red, re-run Disk Utility to see if those error will clear- if they don't reply
back to this post right away and let me know what the exact error message is),
quit Disk Utility.
• Now attempt once again to access the affected documents and files and see if you are able to access these items now.
I hope this helps.