Save as IDML. Do not expect it to be perfect.
New features will be lost or mangled and text is very likely to reflow.
thank you. I've saved an Imdl version just incase but then you always seem to lose the links, very annoying.
If you lose the links it's because they are not available on the machine where you open the .idml. The file itself preserves the links just as they are in the original.