1. Add a comment (like a sticky note) to the page, then save the file. The next time you open it, open the Comments panel and click that comment. It will jump to that page. Make sure to remove it (and add a new one, if you wish) when you close the file, though.
2. Go to Edit (or the Reader app menu if you're using a Mac) - Preferences - Documents and tick the box next to "Restore last view settings when reopening documents".