I started this morning InDesign cs6 on my Mac Pro (with El Capitan) and it needed 10 minutes to start.
Then everything went slow (one shift+W need 2 mins and I was working on a very light file)
I searched for the reason and I thought it was for a corrupted file, trying to be recovered.
I tried restarting the computer, removing the recovery files in the cache folder and then restarting again but nothing happened.
The software is correctly updated.
No error dialog box appear when starting,
really don't know how to solve the problem.
Thank you very much in advance for your help!
Unfortunately four-year-old InDesign CS6 doesn't work well with El Capitan. Problems with that combination of software and operating system are reported here every day.
There will never be a fix for CS6 because it has reached end-of-life. You should either roll back to an earlier version of Mac OS X which supports CS6, or upgrade to a Creative Cloud subscription which does support El Capitan. Sorry.