For example, imagine this scenario: you created an outline with OmniOutliner. You then want your partner to proofread it for you. Sadly your partner doesn’t have access to OmniOutliner. Therefore, you exported the outline to a text file and sent it to your partner. Now, though you have a proofread version of text file, you have no idea how to put it back into your OmniOutliner outline.
If you need to both simultaneously/independantly work on the file , you will need to merge changes through an app with ‘diff’ capabilities… something like a Version Control System like “git”.
yes, but the OP is more concerned with content I think. To keep formatting, one could open the .oo3 file. Inside there is a file name contents.xml. Rename it to contents.zip then unzip it. Edit the unzipped file then rezip it then rename it to contents.xml.