Add contents by simply dragging and dropping your PDF files to Mendeley Desktop. In this way you will import both metadata and the full-text document.
Use the Watch folder option to harvest PDF files from a dedicated folder on your computer. Every time you save a document in the folder, it will be automatically scooped up by Mendeley and relevant metadata extracted.
If the database that you are searching does not offer full-text access or allow for direct export, you may be able to export data on articles, books, and sometime books chapters, via a tagged text format instead. The two most common formats are RIS and BibTEx.
Simply select the data that you wish to import into Mendeley, save it as RIS or BibTEx file on your computer, and use the import option in Mendeley Desktop.
Use the dedicated Mendeley button to export references directly from other Science Direct, Scopus and other Elsevier databases.
If you have a reference list in plain text (MS Word, GoogleDocs, etc.), you can convert this list to Mendeley entries using the text2bib tool.
The result of this conversion depends on your plain text list of references. You will achieve the best outcome, if your list of references follows one of the major reference styles and is well structured.
text2bib translates plain text into BibTex, which can be processed by Mendeley (and other similar systems).
To use text2bib you need to register, which is free of charge.
Get text2bib: http://text2bib.economics.utoronto.ca/