Configuration only — no code on your side.

Group-Office ships a community wopi module that lets you register an office service with an arbitrary address. Register SumOffice there and the documents in Group-Office open in our engine. Measured on Group-Office 26.0: a macro workbook and a document with five pictures went through the full round and came back intact.

What was measured

The round	`.xlsm` and `.docx` opened from Group-Office, edited, saved back as a new version. The workbook took 4.6 s to appear once the editor was warm, 14 s on a cold start; the save came back as version 2 in Group-Office’s own file list.
What came back	VBA byte for byte, all five pictures byte for byte, the edit in place.
What we fixed to get there	Group-Office sends the open request as `multipart/form-data` rather than a plain form post. An editor that does not expect that answers with an error and the frame stays blank. Ours handles it now — worth knowing if you are evaluating any WOPI editor against Group-Office, not only ours.
Microsoft Excel afterwards	Opens the returned workbook silently — no repair prompt. Measured on a real workbook (22 parts, a macro project and a Power Query binding), opened in Microsoft Excel on macOS after the round.
Two things that will stop you	The service address you register must end in `/wopi/` — Group-Office appends `files/<id>` itself, and without the trailing path the editor never reaches the file. And the folder needs write permission for the account doing the editing: on a fresh install `Public` is shared with the internal group only, the save comes back as `403`, and the editor then stops retrying until it is restarted.

Setting it up

# the editors, behind your TLS address
git clone https://github.com/SumOfficeApp/sumoffice-docker && cd sumoffice-docker/nextcloud
cp env.example .env    # PUBLIC_URL=https://office.example.com
docker compose up -d

# Group-Office → the community "wopi" module → add a service
# discovery URL:  https://office.example.com/hosting/discovery

Evaluation is free with no time limit; production is the per-application license — per embedding application, with no meter on your users. The other systems we measured →

Then

Check my Excel file — what your workbooks rely on, in seconds.
Tell us your Group-Office version — 26.0 is measured.