Hello gaylenefromsherwood park,
If you are not able to open a file with a .pdf extension, you may need to change permissions for that file type.
The resource below is for the latest operating system, but the steps will work in Snow Leopard (10.6) as well.
OS X Yosemite: If you don’t have the permissions to open a file or folder
https://support.apple.com/kb/PH19061?locale=en_US
If you don’t have permission to open a file or folder, you may be able to change the permissions settings.
Select the item, then choose File > Get Info, or press Command (⌘)–I.
Click the disclosure triangle next to Sharing & Permissions to expand the section.
Click the pop-up menu next to your user name to see the permissions settings.
If you’re not logged in as an administrator, you may need to click the lock icon
and enter an administrator name and password.
Change the permissions to either Read & Write or “Read only.”
In some cases, the person who created an Adobe PDF document, have locked it so that others can't edit or alter it.
If you can’t change the permissions, contact an administrator of your Mac or the owner of the file or folder.
Take care,
- Judy