The American Psychological Association published its first style manual in 1929 with the goal of making scientific communication easier to comprehend by promoting uniform standards for writing and presentation. Knowing how to properly cite online PDF files is essential for meeting the APA’s writing standards.
In-Text Citations for Online PDF Files
In-text citations of PDF files use the author’s surname and the publication year. If the author’s surname and publication year are in the narrative, you don’t need a separate citation. For example, “In 2005, Goodwin determined his initial results were unreliable.” If the author's surname is part of the narrative, place the publication year in parenthesis. For example, “Goodwin (2005) determined his initial results were unreliable.” If the author’s surname and publication year are not mentioned in the narrative, place the citation at the end of the sentence or paragraph. For example, “A detailed review led Goodwin to conclude his results were unreliable (Goodwin, 2005).” If your PDF file lists more than one author, follow the same pattern as you would for a single author, listing authors in the same order as they appear in the PDF file. If the PDF file you're citing does not list an author’s name, use a portion of the PDF title in place of the author’s name. Use quotation marks around the title. For example, “Findings from later studies were never confirmed (“Verifying Data,” 2009).”
Citing Online PDF Files in the Reference List
The purpose of the reference list is to provide enough detail so your readers can locate your sources on their own. The format for listing your PDF files is, "author’s last name, author’s first and middle initials. (publication year). Title of PDF. Title of Periodical [in italics], issue number, pp-pp [pages]. Digital Object Identifier or URL." For PDF titles, only capitalize the first word and proper nouns. If a digital object identifier is available for your PDF file, use it instead of the URL. Unlike URLs, which can be changed over time, DOIs are permanently assigned to individual publications no matter where they might be moved to on the Internet. For example, for an online PDF file with a DOI, you'd write, "Goodwin, A.C. (2005). Reevaluation of short-term recognition studies. Journal of Cognition, 9, 225-229. doi: 22.1037/0277-59126.96.36.1991." For an online PDF file without a DOI, you'd write, "Goodwin, A.C. (2005). Reevaluation of short-term recognition studies. Journal of Cognition, 9, 225-229. Retrieved from http://ojs.lib.swin.edu/cognition."