Hi Sven, you can use File > Export to write out selected objects only.

But there is not any method to set the page size to fit to objects, there is an option for the opposite of that, making objects fit to the page by using "Scale: Fit to page".

I'm not familiar with LibreOffice Draw but usually there should be a way in a drawing app to import in the contents of a given file while maintaining the current page size.

- Michael