When articles import into Papers they are automatically matched to the metadata so you know exactly what the article is. Sometimes, you may need to rematch metadata. If an item is not matched with metadata automatically on import, you will have the option to "Match" both when right-clicking on the item in your library on the right info panel. Currently, our matcher is only available with references that have a PDF.
When you activate the matcher, it will take a second pass at the paper and try to match it automatically. If it can't, you'll have the option to select part of the metadata visible within the preview that appears to run a search to find a match. Usually just part of the title or any identifier (DOI/PMID etc) will do it.
Other metadata update options
Edit Details will bring up the metadata editing pane, including the PDF preview so you can easily copy the fields to populate the reference.
Clear Details will erase all metadata from the reference. The name will revert back to the original download name. From here you can repopulate all the metadata fields or use "Match" to find a match.
Selecting Update Details will rerun the matcher and populate any missing metadata fields.
Still, struggling? Check out our Matcher Do's and Don'ts when trying to find the correct article metadata.