I have created my google classroom and want to have links the students can access within the classroom. I know how to make a link from a website, but I want to add a document as a link not a website. How do I make a link that will pop up a PDF instead of the whole website or powerpoint?

I not 100% sure but I think if you save/convert the powerpoint to PDF and then save the link that might work. If I understand your question correctly.

Could you upload your document to Google Docs then upload the Google Doc as "view only" by adding it as a material? Students could access your document and you would be able to edit it if needed.