Working in Microsoft Teams lets you work on files together at the same time. Also, messages about the document stay with it and will show up in your team conversations.
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In a team conversation or in the Files tab, select More options
next to the file. -
Chose if you want to edit the file in Teams, on your desktop, or online.
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Edit the file. Colored flags show who else is working on it with you.
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Select Start conversation to add a message about the file.
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Type your message or @mention someone and select Send.
Source: Microsoft