Install the Mac OS X 10.6.8 Update Combo which should re install the Mac App Store for you.
Restart your Mac after the combo is installed.
It's ok to do this even though you are already running v10.6.8.
Unfortunately, the combo updates Safari > Apple Safari 5.1 and Adobe Reader/Acrobat Advisory
You can view PDF's in Preview.
Right or control click a PDF file you have on the hard drive then click Get Info.
Click the pop up menu next to: Open with. Select Preview. If it's not available, click Other. Navigate to the Applications folder, select Preview.
Then click: Change All
If you have the trial version installed, uninstall the software.
Use the native Mac OS X app Keychain Access instead.
/Applications / Utilities
For Glims: Install the latest build: http://www.machangout.com/
For what it's worth, Little Snitch will cause no end of problems and according to Apple, "alters the system". You don't need it.