You can add files to Mendeley by:
Export references directly from other Elsevier products such as Science Direct or Scopus to Mendeley by:
The Sync function will synchronize your library data to Mendeley Web, Desktop, and Mobile.
To edit Sync options, select All Documents in your Mendeley Desktop library. Then selectEdit Settings to choose to have all documents or specific folders synced to your Mendeley Web account. Being selective about what you sync will help you stay within your Web Space storage limits.
Mendeley Institutional Edition users can now try out "Mendeley Suggest" which suggests new papers based on your library.
Try it today by clicking "Mendeley Suggest" which is located on the left panel below "Literature Search".
Install the Mendeley Web Importer -- Install the Web Importer into your favorite web browser to import references and documents from academic databases.
Save articles to your Mendeley Library as you browse.
You can have Mendeley 'watch' certain folders on your computer, then as PDFs are added to these folders they get imported into Mendeley automatically. Choose File - Watch Folder in Mendeley Desktop.