You do not need to memorise APA style!

Keep the APA guide close and refer to it regularly throughout your studies. Here are the key links:

Some key concepts for understanding APA style and using the guide:
Concept and explanation	Examples
Source = A source is the origin of information, knowledge, and/or ideas.	Author, researcher, lecturer, organisation, journalist, influencer, etc.
Source material = What is communicated - orally, in writing, or digitally; i.e. the actual content of the information	Theories, findings, arguments, statistics, reflections, or conclusions presented in a source
Work = The document type (physical or digital) in which the source material is published.	Book, newspaper article, journal article, website, video, podcast, TV series, social media, slide deck (PowerPoint), etc.
Reference = The combination of information about the source and the work, presented accurately enough that others can easily locate the same information you have used.	References are collected in a reference list.

A PDF is simply a file format, it does not determine how you cite something. What matters is the type of work it contains: