Mendeley's file organizer can automatically rename your PDFs and file them in a clear folder structure, making it easier to find your files outside of Mendeley. Open Mendeley's File Organizer which can be found under Tools > Options.
In the tab, you can select:
1. To organize your references, use folders. Click on Create Folder… to create a new folder, give it a name, and hit Return.
2. Drag references from the center column on to the Folder to add them.