Method One - Drag and Drop: You can drag and drop PDFs into your library and Mendeley will extract the document details (bibliographic data). Simply have the Mendeley Desktop window be small enough that you can find the file you want to add, grab it with your cursor, and drag it into the empty space in the middle of the Mendeley progaram. You can also drag entire folders into this space.
Method Two - use the file menu, or the 'Add files' option and browse to the PDFs or folders you want to add.
When adding any files, double check the document details (on the right side of the screen when you select a document) as it can be incorrect. Simply click in the field that is incorrect and make your corrections
Mendeley can easily import references from other reference management softwar (EndNote, Zotero and similar programs) or from files of citation lists saved from databases.
Step 1: Export your files from the other software into a Research Information Systems (.ris), BibTex (.bib), EndNote XML (.xml), or Zotero Library (zotero.sqlite) format.
Step 2: Open Mendeley and create a folder for the documents you want to import.
Step 3: Highlight your folder and click on "Add Files" icon.
Step 3: Find the location of your previously exported file and select it.
Your documents will be imported into the folder you had highlighted.
Repeat these steps for each file you need to import to Mendeley.
Search the Mendeley Catalog.
Add Entry Manually is always an option. Simply select this from the "add files" or "File" menu.
Use the Web Importer. For a selected number of sites, mostly in the sciences, the Mendeley web importer seamlessly pulls content into the web version of your library. Syncing your library then move the reference to the desktop version.
Watched Folder. Set your Mendeley Preferences to automatically add new PDFs that were saved to a specific folder.