Comparing

Track Changes can also be achieved using the Compare Document feature.
It is possible that track changes were not switched on before a document was reviewed.
In this scenario you can reproduce the track changes by comparing the original document with the document that has been reviewed.
When you have finished you will have a document that includes change marks where any changes (and optionally any formatting changes as well) were made and are highlighted.

If you run Compare Documents and either of the documents contain tracked changes then you will get the following warning message appear.
SS

Lets say for example you have a sentence in your original document that was deleted in the "tracked changes" document but altered in the "compare" document
What will Word actually do ?
Word will show the sentence as deleted, but that doesn't accurately reflect the changes contained in the "compare" document
What happens ???

If you have two documents both containing changes it is possible to compare and merge the two to create a "revised" document.
The "revised" document will contain all the changes as "tracked changes".
Any tracked changes in either document are accepted first.

Compare and Merge documents dialog box
SS(merge) + SS(compare)

Merge - This opens the document you select in the dialog box and merges the changes from the active document into it.
Merge into Current Document - This merges the changes in the document you select in the dialog box into the active document.
Merge into New Document - This merges the active document with the document you select in the dialog into a new document.
Legal Blackline - Creates a new document showing the insertions and deletions. Changes the button to Compare
Find Formatting -

Revised document - this is the modified document that contains the merged changes
Original document - this is the document you are comparing against.

Random Number
To enable word to track all the changes made to a document every change is assigned a random number.
To ensure that you get an accurate revised document make sure that the "store random number to improve merge accuracy" is selected
SS
Tools > Options > Security tab.