An online source may appear as an abstract, an excerpt, or a full-text article or book. It is important to distinguish among these versions of sources and to use a complete version of a source, preferably one with page numbers, for your research whenever possible.

Abstracts and excerpts are shortened versions of complete sources. They often appear in database results for articles and books or in search engine results for Web sites. Both abstracts and excerpts are brief (usually fewer than five hundred words) and can provide enough information for you to determine whether the complete source would be useful for your paper—but they generally do not contain enough information to function alone as sources in a research paper. Reading the complete article is the best way to understand the author’s argument before referring to it in your own writing.

A full-text work may appear online as a PDF file (portable document format), as an HTML file (formatted for display on the Web), or as a text file (a simple format that you can read within a word processor).

A PDF file is usually an exact copy of the pages of a periodical article as it appeared in print, including the page numbers and visuals. Some corporate and government reports are presented online as PDF files, and these too are usually paginated. PDF files are useful because they can be printed or annotated.

A full-text document that appears as an HTML or a text file may or may not be paginated. If it’s available, choose the PDF file for your research because you will be able to cite specific page numbers.