We often get questions about what to do with a PDF file found on the internet (either through a search or from a website). PDF is a file type--just like Word or Excel are file types--that preserves text, formatting, and graphics. PDFs display various types of content, such as brochures and reports.
Luckily, most PDFs you will want to use for school assignments and/or papers will clearly show the main information you need for any citation: Author, Date, Title, and Publication Information.
And since you will almost always find a PDF on the internet, you'll want to include a URL:
Author's last name, initials. (date of publication). Title of document. Site name (if different from author). http://Web address.pdf
Rohrig, M. (2018). A resource for healthcare professionals: Physical therapy in multiple sclerosis. National MS Society. http://www.nationalmssociety.org/NationalMSSociety/media/MSNationalFiles/Brochures/Clinical_Bulletin_Physical-Therapy-in-MS-Rehabilitation.pdf
Office of Juvenile Justice and Delinquency Prevention. (2020, July). Highlights from the 2018 juvenile residential facility census. https://ojjdp.ojp.gov/sites/g/files/xyckuh176/files/media/document/DataSnapshot_JRFC2018.pdf