A track changes document can seem a bit daunting, so an author will normally receive a clean copy document as well.
What do these documents look like?
In the examples below, I’ve described what I do as a beta reader, copyeditor and proofreader in a rather flowery way.
1 My original document.
2 My track changes document, with my changes marked in red.
3 My clean copy document, with my changes made but unmarked.

Both track changes and clean copy documents show any comments which explains why specific changes have been made. Comments can be made to query elements that are unclear or to ask for a decision to maintain consistency. For example, if a word is spelt two different ways and there is no obvious majority. In this example I’ve made changes for clarity and concision.
It’s worth repeating that there will always be a level of subjectivity to any changes or suggestions and the author has the ultimate decision to accept or reject them as they see fit.