Whether it is a good idea to attach a template depends on what you are trying to accomplish. Attaching the template ensures that the document gets access to keyboard shortcuts, building blocks and macros that are stored in the template. You can use the "Automatically update document styles" to update the styles (and their formatting) in the document.

However, if you want a document to adjust to the layout and content of a different template, creating a new document based the template and importing the existing content would be a better idea.

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional