(Corrected:) I found that, to preserve the MS Office Recent Document list, all I had to do was UNcheck the Office application.
In the past, it seemed like I had to also exclude the office Recent folder, but as of 12/20/2014 with CCleaner 5.01 that is not needed.
You must have the application MS Office UNchecked. To do this, in CCleaner, select the Applications panel (click on "Applications" near the top of the window beside the word "Windows"), then scroll down to find its "Applications" section (below Windows Store), and UNcheck "Office 2013" or whatever your office is.
[i may be wrong about this, but it seemed like I had to check this Office 2013, run a clean and then UNcheck Office 2013 to make it work right, but that seems wierd.]
Other settings do not appear to matter. You can have "Windows Explorer - Recent Documents" checked or not, It does not matter (that clears the ...\AppData\Roaming\Microsoft\Windows\Recent folder and not the Office\Recent folder). Same is true for "Windows Explorer - Other Explorer MRUs", and "Internet Explorer - Recently typed URLs" - they do not matter as far as preserving the Office Recent Document list is concerned.
So the following folder exclude does NOT need to be done (at least not anymore) ...
In CCleaner Select: Options, Exclude, Add, Folder, and browse to the following...
C:\Users\YOURACCOUNT\AppData\Roaming\Microsoft\Office\Recent\*.* and choose "All Files" (which tacks on the *.* above).
[substitute your account name for the YOURACCOUNT place holder].
FYI, I could not make CCleaner successfully exclude specific file types within the Recent folder - file types like *.xlsb or *.xls* or *.xlsb.LNK did not work.
Which is a shame, because there can be a lot of links in the Recent folder that I would like deleted, but I found no way to preserve just the types I wanted to keep.
[At one time, I thought I also had to exclude the file ...Local\Microsoft\Windows\INetCache\Low\SuggestedSites.dat, but that turned out to be wrong too.]