In OSX, I want to get the filesoutside the application sandbox in the application. Is there any way to do this?
Yes, there is a way:
First of all, your app need the files.user-selected.... entitelement.
Keep in mind, that there always has to be a fileopen dialog to gain the rights to a specific file outside your app sandbox.
Second: This rights only last for a session. If the user closes your app, the rights are lost, unless you create and store a security-scoped -bookmark.
Take a look here: