Mendeley have a few options available for adding your existing PDF documents and growing your personal library:
Adding entries manually is often necessary for reports, websites, books, and other reference types.
Articles can often be added from databases, Google Scholar, or by dragging and dropping PDFs. However, if these options do not work, you can create a manual entry.
To create a manual entry, follow the steps below:
You can add PDF documents as well as their references simply by dragging and dropping the PDFs into your Mendeley Desktop App:
This will have to be done individually.