I am writing about something within the folder named "Documents library" (Windows 7).

This folder is accessed thus: 1) Click the "Windows" button in the lower left corner of the desktop. 2) Then click "Documents".
One of the sub-folders in that folder is "Adobe Acrobat Document". Currently, if that folder's name is lightly moused-over then one sees a message appear stating: "File count: 345 / Size: 724 Mb". That is correct, I know, because recenlty I had seen those files listed in that directory. However, when I now open this folder I see "This folder is empty". What's happened, please? The actual PDF files are still on the computer (and opening okay using Acrobat Reader 9.3) but the "Library" is no longer finding and displaying PDF files. Other file types are showing fine within the 'Documents library'.