Poatmyp (“POint AT MY Pdf”) let multiple people look at the same PDF (slides, most often) and share a pointer on the slides. Everyone can go back and forth in the document. It's like screen sharing, except it's clear what you share and what you don't share.
To use it, upload a PDF. You will be redirected to a URL, at which you will see (after a brief while) the first page and a sidebar with thumbnails of all the pages; click on one to jump to the page; you can also go forward an backward using the space bar and the backspace key.
You can self-host this program. The (public domain) source is at poatmyp. See the README there.
Data protection: Except for a brief moment during rendering, all data put in here is in RAM and will be discarded about a day after upload. We don't keep logs on disk (it's conceivable someone might look at console output, for instance during debugging). Don't share confidential slides (unless self-hosting): The URLs here are too short to not be guessable.