Your only potential recourse is to hold down the shift key while launching Pages, and then try to open that document again. Because a crash occurred, the document most likely is corrupted, and useless.
Maybe its time to clear out System caches, and temporary files, rebuild the font database, and scan your drive for errors. You can do all of that automatically by booting into Safe Boot mode. Reboot normally, and afterwards, try opening that document one more time. See if your El Capitan stability improves after a Safe Boot.
You should not be running any form of anti-virus, or any so-called Mac Cleaner applications, as the former is unnecessary (no viruses on the Mac), and the cleaner apps are all to frequently too aggressive and remove important parts of applications and the OS. The Mac has its own security processes running behind the scenes, and the anti-virus software interferes with it, causing pandemonium.
There is an increasing volume of malware being written for the Mac, and I use the free version of this anti-malware application myself without any association, or compensation from the vendor.
