Merging .CHMs using RoboHTML version 7

Not as "drag 'n drop" as version 2000. It requires that you use MS HTML Help Workshop for the final compile.
http://msdn.microsoft.com/library/tools/htmlhelp/wkshp/download_main.htm

1. Use RoboHTML to compile your Master chm and Sub-chms.

In my example we'll use
Master.chm
Book2.chm
Book3.chm

2. In Windows Explorer, copy and paste Book2.chm and Book3.chm. into the Master.chm project folder. 

(do not include companion .hhc files as we do .cnt files in Winhelp <g>.)

3. Use Notepad to open the Master.hhc file and use copy and paste to edit
the file.

The code needs to be inserted at the bottom of the hhc file but above the closing </HTML> tag. Do the same thing for Book2.chm and Book3.chm. (Obviously, you change the Book2.chm and Book2.hhc for your own file names.)

<OBJECT type="text/sitemap">
<param name="Merge" value="Book2.chm::/Book2.hhc">
</OBJECT>
<OBJECT type="text/sitemap">
<param name="Merge" value="Book3.chm::/Book3.hhc">
</OBJECT>

4. Save and close the Master.hhc file.

5. Open the Master.chm project in the RoboHELP HTML Editor. 

Go to the File drop down menu, click on Project Settings. When the dialog box opens select the Index Tab, and put a check in the Binary Index check box.  Click on the Compile Tab and add Book2.chm and Book3.chm to the Merged Files box. Close the Project Settings dialog box, save and compile the Master.chm project.

7. Open the .hhp for the Master Project in Notepad. 

Under [MERGE FILES] remove the path statement to each chm, leaving only the name of each chm.
Under [FILES] remove #BSSC to avoid an error message when HHW does the final
compile.

8. Now, open the Master.chm project in Microsoft HTML Workshop to do the final compile of the Master.chm project.  Open it and take a look.

Consider yourself merged!