I find OO3 in DTTG can be opened in OO for iPad.
Then, the OO file can be open in DTTG after some editing. All sound good.
The problem is when DTTG is synced with DT, the OO file edited is not an OO file format anymore. The file appears as a folder in DT and finder and DTTG (after sync). So the file can not be opened in OO for Mac.
Over here, for OO3 files, DTTG says “Document cannot be displayed”. They can be sent to from DTTG to OO iPad, edited there, sent back to DTTG, and synced from DTTG to DTPO. But the edits are missing. The format is still OO3.
You seem to have a slightly different result – i.e., edits are not lost in transfer. I don’t normally use this route to get documents to/from OO iPad, so I’ll defer to your experience. Note, that OO3 documents are packages - a type of folder. If the package does not have an “oo3” extension, then the file system (and DEVONthink) will not know that this is an OO3 document.
When you transferred the document from OO iPad to DTTG, did you select “OmniOutliner” as the file format? If not, then the file will probably not transfer correctly to DTTG (and from there to DEVONthink on the desktop).
I indeed saw that oo3 file synced back to Devonthink (Mac) through DTTG appears as oo3 file format as you mentioned. But in some case i still see oo3 files’ format are lost in certain situation. Unfortunately I can’t distinguish the difference between these two occurrences.
But still, in those cases when an oo3 file is synced back well, my editing was lost as you mentioned. Therefore, this route (oo3 ipad - DTTG - DT - oo3 mac) seems not feasible for now.
BTW, you can turn an OO3 folder (i.e., without the .OO3 extension) back into an OO3 document by just adding that extension on the desktop. Don’t do this while the file is stored in DEVONthink however because it will become an orphan and a minor pain to fix. Put it on the desktop, change the extension, then import it back to DEVONthink.