Can you tell us where you saw this CHM file?
My own guess here is that what you saw was someone's idea of demonstrating to their user where a change occurred. I know of no tool that would automagically mark up a CHM file in this way.
Many thanks for your email.
Do you know if there is a way RoboSource Version control can highlight the updated content ? I have been trying, however, not much luck.
To the best of my knowledge a source control system is only going to tell you which topics have been modified, not what the changes are.
If you are the only author, then the Topic List can show the modified date of topics. If you are working with others, your Topic List will only cover what you have edited. Not sure if the source control system can give you dates modified. I would think it can as it is all about dates.
As to the exact content, I think you will find that is down to you. If you are referring to just flagging changed topics in the TOC of a CHM, I'll hand you back to Rick as I believe that can be done and he will know how. That is not the same though as marking the actual changes.
See www.grainge.org for RoboHelp and Authoring tips
A source control system can show what files have changed and the changes that were made in the source, For example, here's a screenshot of a help topic in our source control system we use (Mercurial):
In a particualar recorded change (called a changeset in Mercurial), the old text from the previous version is in red and the new text added in this changeset is in green. I think I remember seeing RoboSource control could do something similar.
I don't know if there's a way of visually comparing two chms, but I have seen utilities out there that compare two htms visually. Like this one: http://www.htmlmatch.com/
Perhaps it can handle the specific htm pathway in a chm. I don't know.
Certainly this may work for the individual files, but the OP was asking about depicting changes inside a compiled CHM. Are you saying this also works for compiled CHM files?
With regards to my comment on source control, I was responding to Peter's comment on souce control. My example there uses the RH source files, not generated CHM files.
If you're referring to htmlmatch.com, I don't know if it works for two chms. Probably not. Once you extract them, it'd work. You could compare individual htms that way.
That said, here's possibly a workaround though. I see a utility inside Helpware's very handy FAR HTML software that lets you compare two CHMs.
You associate a diff viewer (BeyondCompare or some other tool, maybe even the above htmlmatch), and you can then compare two chms and see a list of differences that way. Obviously, it's not the same as seeing the diffs inside an actual chm, since under the hood, it's really just extracting the chm files into a temp directory and comparing the resulting htms, but still, it might be worth looking into.