You can add a reference citation to Mendeley in at least 5 ways. Here's how:
1. Drag and drop PDFs or other files from your computer directly into the All Documents folder of MY LIBRARY.
2. File > Add Files/Folder, then use your computer's Finder (Mac) or Browse box (PC) to search for your folder or documents.
3. File > Add Entry Manually to type or paste your citation data into Mendeley Desktop.
4. File > Import to import data in various formats: BibTeX (*.bib), EndNoteXML (*.xml), RIS (*.ris), or Zotero Library (zotero.sqlite).
After importing, it is extremely important that you review and edit the metadata (title, author, etc.) for your entries. This will insure your Works Cited pages and Bibliographies are generated correctly. Be sure the Type (Journal Article, Book Section, etc.) is correct for the document or citation you are importing. If the Type fields do not include something that you need for a certain citation style, edit the Type template by going to Mendeley Desktop > Preferences > Document Details. Check the fields you want to appear on a certain Document type template. For example, you can add a 'Medium' field to the Journal Article Document Type so that you can comply with MLA style and add 'Print' or 'Web' as needed.
TIP: You can also import references from another citation manager. After exporting the data from your old citation manager, you can drag and drop the .xml file into your Mendeley Desktop.
To import your EndNote library, you need to first export your references to an 'EndNote XML' file and then import that into Mendeley Desktop.
In addition to the EndNote XML format, you can also export references to Bibtex and RIS format in EndNote which Mendeley Desktop can also import. In EndNote select Edit > Output Styles > Open Style Manager. Check the 'Bibtex Export' and 'RefMan (RIS) Export' options in the list that appears then close the window. Then go to File > Export... and select the 'Text File' type. In the box labeled Output Style, select either Bibtex Export or 'RefMan (RIS) Export'. In the filename field, enter a name ending in ".bib" for Bibtex or ".ris" for RIS export and click 'Save'.
Please bear in mind this will not add your files to Mendeley Desktop, only the references. To add the PDF from RefWorks to Mendeley you will need to download them manually and add them to Mendeley.
For other citation managers, check the Mendeley Support page for information and assistance.
If you're having trouble importing PDFs along with References, you could move all of your PDFs to a Mendeley Watch folder that you have set up, but you may need to merge (de-duplicate) all the citations or clean up the metadata (citation information).