Within Teamwork.com, you can lock a file in a project to prevent other users from editing it.
Go to the Files area of the relevant project and locate the relevant file.
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Click the dropdown arrow to the right of the file you wish to lock and select the Lock option.
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Alternatively, you can click into the file itself and then choose the options button (three dots) to the top right of the page and select the Lock option.
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To unlock a file, click the blue key button to the right of the file name in the list of files.
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If you are viewing an individual file, the blue key option will appear beneath the file name.
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Note: Only site owners/administrators and project administrators can lock or unlock files.
For more information see: Uploading Files in the Files Area