Snapshot tool using Adobe Acrobat on a secured file

When attempting to use the snapshot tool (camera icon) to select parts of a .pdf for a journal club paper today, I ran into an error. The highlight square would appear, but the area would not get copied to the clip board, so I could not paste it into my presentation. I had downloaded the paper from the journal's website, and it had some security enabled that resulted in it saying "(SECURED)" in the title bar, next to the .pdf's name:

The problem occurred in both Adobe Acrobat and Reader. To fix it, I clicked on the lock icon in the left menu (Security Settings) and then clicked "Permission Details" (see above screenshot).
This opened the "Document Properties" dialogue box to the "Security" tab. Here I chose "No Security" from the drop down "Security Method" menu (see screenshot below), click OK, and voila--the snapshot tool worked!