adding something on a map/photo

You can add circles and text annotations to PDFs using Apple’s Preview. In the Scrivener Binder, right-click on the PDF you wish to edit and select Edit in External Editor. In Preview, you’ll want to choose the Oval Annotation tool, which is located in the Tools menu, under Annotations. With that tool you can draw circles on the page. Incidentally, the Text Annotation tool allows you to add bits of commentary to a PDF, too. Once you’ve made whatever markings you want, just save the PDF and close it. Back in Scrivener, you’ll have to reload the PDF (just click on some other document and then back) for the changes to show up.

Easy as that; you are out of luck with arrows though – at least with Apple Preview.