Default - "Open Read Only" for Office Files

I recently worked on a template solution for one of my projects and explored every possible option. Unfortunately, there is no tenant‑level, site‑level, or library‑level setting in SharePoint or Microsoft 365 that makes all Word/Excel/PowerPoint files open in read‑only mode automatically.

Microsoft only allows per‑document read‑only settings, not a global default.

Option 1: Use a .docx Template

You can upload a .docx file as a template using Add Template in the library. If you set the template document to open as read‑only inside Word before uploading it, that setting becomes available for every new document created from the template. This works because .docx templates allow new files to inherit those properties.

Similar solution explaining in - Sharepoint - Prevent a new version each time a document is read | Microsoft Community Hub

Option 2: Enable “Require Check Out”

You can turn on Require Check Out under Library Settings > Versioning Settings. This forces every file to open in a read‑only state until a user checks it out. The only limitation is that co‑authoring and real‑time collaboration by multiple users will not work, because only one person can check out the file at a time.

Option 3: Use Power Automate to Set Read‑Only After Creation

You can build a Power Automate flow that triggers whenever a new document is created in the library. The flow can automatically update the file’s properties or apply a protection setting (such as marking it read‑only or restricting editing). This ensures every newly created document gets the read‑only setting applied consistently. The only limitation is that this applies after the file is created, not at the moment of opening.