In SharePoint Designer 2007 you can simply open up any type of file you wanted even if it did not reside in SharePoint. Well now things have change for 2010… Now you are forced to open up a SharePoint site before attempting to open up a file that resides outside of SharePoint. If you try before opening up a site you get the following error message: “You must first open a Web site before editing external Web pages…” Not really sure why they changed this maybe they want to ensure that you are not downloading the free SharePoint designer and simply using it as a HTML editor for non-SharePoint sites…
Anyways that is not the focus of this post. I also noticed that SharePoint designer tricks you to thinking that you cannot edit pages. Say you want to modify a file that does reside in SharePoint. By Default it will open up in a read only view (HTML) and will not allow you to change the file. It will have a orange like highlight to areas that are not editable.
So the trick is to right click on the document and choose the option “Edit File in Advanced Mode”.
Now you can edit the file as you wish!
Hope this helps! If you know of a better way please leave a comment.