If you have imported a PDF file, and find that it is wrongly labelled, or that no metadata has been entered for the article at all, please try the following steps:
1. Copy and paste the correct article title from the PDF into the title field in the Details tab
2. Right-click (Cmd + click for Macs) on the document in the central library list and select Mark As -> Needs Review
3. In the Details tab, click Search by Title which will look for a match in the Mendeley Catalogue (as of Mendeley 1.13).