When you open an e-mail attachment in Word it may display in reading layout view or it may open in Protected view. Both of these settings affect what you see in the document.

Note that if the recipient is using Word 2013, what you describe (lines in the margin) is the default display for documents with tracked changes. It's the so-called "Simple Markup" view, selectable via the Display for Review drop down on that version.

To ensure that a recipient sees exactly what you see, you will have to convert the document to PDF (with tracked changes enabled) and send the PDF instead.

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional