To find out how much you have free on your hard drive open it as a window:
Finder > Menu > View > Show Taskbar > at the bottom of the window it should say XX available
OSX is happiest with 20% free on your hard drive, very low free space makes it constantly attempt to write to whatever is available and go bog slow.
If you don'y have much room left back up what you don't currently need and delete that off your hard drive.
As a reminder, we are experienced Mac users that are volunteers in this forum, and not Apple employees or subcontractors.
The > About This Mac panel tells you how much physical memory is installed in your computer -- not how much remains.
Like any other operating system, Mac OS X has continued to evolve and gain more complexity in the process. It isn't written anywhere that you should perform periodic preventative maintenance within the operating system and yet, this is necessary to retain optimal usage. And, as focused as your anger at losing that document, know that this could have happened on Windows, or Linux on non-Apple hardware. We have all learned hard lessons and learned to trust frequent document saves and backups.
Your issues may have to do with system file permissions and fragmentation -- not of the hard drive, but the indexes that point to all the files on your machine. If it is solely these issues, then there are relatively simple procedures to correct them, and lead to improved performance that you will notice.
First, you need to verify/repair System file permissions outside your login directory. You would launch Disk Utility from the /Applications/Utilties folder. Select your boot drive -- probably called Macintosh HD. Select First Aid, and do the verify/repair. Good idea to run verify on your drive while in that panel location. Then exit Disk Utility. You should get in the habit of this procedure each time you install Apple applications, system software updates, or third-party applications.
Second, you need to boot into Safe Mode. Power off the laptop. Press and hold the shift key. Power on. When you see a grey horizontal progress bar, release the shift key. When you get to the login window, do the obvious and before clicking to login, press and hold that shift key again until your desktop and Finder menu bar appear. You might try Pages here to see if former issues remain, otherwise you need to reboot normally to resume full use of the machine. This process is something you may choose to do on a monthly or quarterly basis.
Evaluate if the two above procedures have improved your machine behavior.