Window > Editorial > Track changes.
The tracked changes are visible only in the Story editor (Ctrl+Y), and record only to content changes, not formatting.
Acrobat has strong PDF editing abilities. One advantage is that the original files aren't at risk for inadvertant changes. Search Google for terms like "track changes in acrobat pro and acrobat reader" without quotes, for details.
One disadvantage is that changes in the PDFs must be brought into the original files.
The commercial InDesign plug-in Annotations for Adobe InDesign - DTP Tools, can import changes from an edited PDF into the source InDesign file. From their info: "Now you can load PDF notes right into your InDesign layout. Annotations plug-inallows you to import notes and comments from PDF into a source InDesign file." There's a trial.
I'm editing someone else's work, how do I track changes so that they can read the original and my proposed change in the same document?
There are two plugins that will show the track changes in PDF and on screen.
There is a free script to navigate the track changes.
All the best.
Checked this script and looks meeting our requirement and please confirm to 'enable' track changes in InDesign before running this script.
You will need to manage InDesign track changes.
If you use a lot of track changes in your work, you might want to check this script out.
It displays the changes in a list, navigat to the change by clicking on the list.