Most PDFs open directly in the browser, so you can read them online. These PDFs have permanent URLs which you can put into your reference list as you would a website.
However, If you can only view it by downloading it from a web page to your computer (meaning the URL will be irretrievable for your reader), reference the URL of the page you downloaded it from and include [PDF] in square brackets to indicate to your reader that the information is not taken directly from the site listed. For example:
Author, A. or Corporate Author. (Date). Title of PDF in italics [PDF]. Retrieval information
Example—reference list entry
Nursing Council of New Zealand. (2012). Code of conduct for nurses [PDF]. Retrieved from https://www.nursingcouncil.org.nz/Public/Nursing/Code_of_Conduct/NCNZ/nursing-section/Code_of_Conduct.aspx?hkey=7fe9d496-9c08-4004-8397-d98bd774ef1b
Example—in-text citation (first)
The Nursing Council of New Zealand (NCNZ, 2012) suggests that... (p. 12)
or
... (Nursing Council of New Zealand [NCNZ], 2012, p. 12)
Note: In the second and subsequent citations, simply use the NCNZ abbreviation, date, and page number(s) (see abbreviations/acronyms for corporate authors).
Similarly, when you use information such as a dataset that opens separately from a website, include the URL the dataset was retrieved from and indicate in [square brackets] the format.
Author, A. or Corporate Author. (Date). Title of data set in italics [Data set]. Retrieval information
Example—reference list entry
Statistics New Zealand. (2013). 2013 Census population and dwelling tables—regional council area, territorial authority area, and Auckland local board area [Data set]. Retrieved from http://statistics.govt.nz/Census/2013-census/data-tables/population-dwelling-tables.aspx
Example—in-text citation
Statistics New Zealand (2013) data demonstrates... (p. 6)
or
... (Statistics New Zealand, 2013, p. 6)