Answer from Purdue Online Writing Lab (OWL):
https://owl.english.purdue.edu/owl/resource/560/10/
Online Lecture Notes and Presentation Slides
When citing online lecture notes, be sure to provide the file format in brackets after the lecture title (e.g. PowerPoint slides, Word document).
Hallam, A. Duality in consumer theory [PDF document]. Retrieved from Lecture Notes Online Web site: http://www.econ.iastate.edu/classes/econ501/Hallam/
index.html
Roberts, K. F. (1998). Federal regulations of chemicals in the environment [PowerPoint slides]. Retrieved from http://siri.uvm.edu/ppt/40hrenv/index.html