Q. What's the difference between HTML and PDF format?

HTML format of a journal article gives you all the words from the original article, with none of the original formatting. There are no headings, no columns, no graphs, and no page numbers, just straight paragraph format to scroll through. This format works well when you are simply reading the article online.   

PDF articles are encoded in Adobe Acrobat format. You will see the article as it appeared in the original print format: all illustrations, charts, graphs, and page numbers are in their original locations. When printed, they look like photocopies of the original articles, and, since page numbers are in the original places, PDF articles are much easier to cite in your bibliography or cited works page. 

If given the choice in a database, always view articles in the PDF format.