Google is hoping to lure more users of Microsoft Word onto their platform. They have recently made some changes to Google Docs that will basically convert Word's tracked changes into Suggested Edits.
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While you no longer have to convert Microsoft Word files to Docs (thanks to the recent Quickoffice integrations), if you do, any tracked changes in a .docx file will be automatically carried over to Docs as Suggested Edits. Once you've imported your changes, you can begin immediately collaborating with your colleagues in real-time.
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