With Outlook (2010/13) it’s a breeze to edit SharePoint documents, even when you’re not logged onto the site. While in the library containing your documents, click on the Library tab and choose Connect to Outlook. Documents will begin to synchronize with a new folder in Outlook.
The bad news is while you’re editing it offline, someone else might be editing it online! To avoid the problem, Check Out the document on SharePoint. That way others can read, but not edit the document. If you think this is too risky or inconvenient you can adjust library settings not to allow offline editing.