I also have/had a lot of trouble finding a good RICHED20.DLL for my purposes. When I found one that works correctly with a certain feature it gave me trouble with another one. Ultimately I settled with a version 3.1 subversion 5.31.23.1230 (which came with a update in Windows 7 or 8 ).
To give you an indication of the versions I tried (for my needed feature-set, which might be different for you) here is my RICHED20 directory with different versions:
How to prevent crashes when pasting into the text editor - Kinook Software Forums.url
MSFTEDIT - (v7.5) 10.0.10240.16386.dll
Probleem-versies.txt
RICHED20 - (v3.0) 5.30.23.1230 (winXP).DLL
RICHED20 - (v3.1) 5.31.23.1229 (win7).DLL
RICHED20 - (v3.1) 5.31.23.1230.DLL
RICHED20 - (v3.1) 5.31.23.1231 (win10).DLL
RICHED20 - (v4.0) 5.40.11.2210 (OfficeXP).DLL
RICHED20 - (v5.0) 5.50.99.2050 (Office2003).DLL
RICHED20 - (v6.0) 12 MSPTLS.DLL
RICHED20 - (v6.0) 12.0.6606.1000.DLL
RICHED20 - (v6.0) 14 MSPTLS.DLL
RICHED20 - (v6.0) 14.0.4750.1000.DLL
RICHED20 - (v8.0) 15 MSPTLS.DLL
RICHED20 - (v8.0) 15.0.4420.1017 (b) msptls.dll
RICHED20 - (v8.0) 15.0.4420.1017 (b).DLL
RICHED20 - (v8.0) 15.0.4420.1017.DLL
RICHED20 - (v8.0) 15.0.4659.1000.DLL
So you could try the 5.4, 5.5 or even 12 through 15 versions.
You can take some of the versions from Office or later Windows-versions.
I think versions above 12 need MSPTLS.DLL too but below that only RICHED20.DLL is needed.
You can also download some of these here (the >12 have MSPTLS.DLL also included):
http://www.kinook.com/Forum/showthread.php?t=2853You can see that the version you've got (5.30.23.1230) is a
very old one (XP) and even 3.0 at that. I would certainly go for at least a 5.31.x version (which should still work on XP). Just copy the RICHED20.DLL to your .exe directory and it will be used. If the 5.31 doesn't have the feature you need you can go to the higher versions until you get the right one
Yeah... picking the right one was a real challenge because in some versions certain bugs where introduced which where solved in earlier versions... but if you don't use certain things you might nog even encounter these bugs.
Also the absolute last version might not work on XP anymore but you can test that yourself.