Q. How do I find an article's DOI?

The Digital Object Identifier (DOI) of an article is usually listed on the PDF or the web page of the article. All DOI begin with 10, so it should look something like this: 10.7717/peerj.4903in URL format, it will look like this: https://doi.org/10.7717/peerj.4903

If it is not mention anywhere in the PDF or the webpage, you can use Crossref's "Search Metadata" search bar or Crossref's Free DOI Lookup to find the DOI.