I am looking for an app that allows me to annotate PNG exports from design apps in another environment i.e. draw arrows, explain things, while keeping the original design as an external file reference.

I would prefer if the app has an “infinite” canvas feature, where you can resize the app to the size you want.

You should be able import files and have the option to update them if they change. You should be able to do this in batch e.g. import a bunch of PNG exports and all the references update.

You should be able to share the output as a PDF or even better online in a collaborative viewing environment. The awesomest would be an environment where multiple people can work in, live, on the internet, but I could deal with PDFs.

This would be used to compare software implementations with designs, but also to deliver flow documents about how to go from one screen to another.

I realize this is a very specific question but hopefully there is something out there. I tried OmniGraffle, Indesign, Figma, Mural, LucidCharts and Illustrator so far but these only do parts of what I need.