People can suggest edits on a Google Doc when they have Comment or Edit access on a document. Suggested edits are Google Docs version of track changes. If you upload and convert a Microsoft Word document with track changes to Google Docs the track changes will become suggested edits.
Step 1 - You must be in 'Suggesting mode' to make suggestions. To do this, click the 'View' menu and click 'Mode' then 'Suggesting'.
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You can also access it from the pencil icon on the right of the toolbar.
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Or from the 'Suggest edits' button to the right of the page.
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Step 2 - You can now make edits, as you do this you will see a green box around the new content you type.
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Step 3 - These suggestions can then be approved or declined with the tick or cross icon.