I found that CCleaner doesn't any more detect files located in C:\Users\USERNAME\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup if they have the extenesions: bat, cmd, pdf, doc, txt.
First 2 file extensions are very dangerous, but also pdf or doc are so, if those files are exploiting some bugs in their assigned software's for opening.
PS: Those file extensions are the only one that i tested on CCleaner v5.19.5633 (64bit), but i think it could be more.
Ccleaner is not an anti-virus or anti-malware programme.
It is a junk cleaner. (Cleaner = Crap Cleaner).
It clears out cookies, caches, saved forms, saved logins, etc.
If you want to check for and remove 'dangerous' files on your system then I recommend that you go to Malwarebytes.com and get their anti-malware scanner.
While you are there get the anti-exploit as well. (And possibly the Junkware Removal Tool).
None of the above are anti-virus programmes, choose one of those yourself.
If you use Ccleaner, in conjunction with an AV, and regilar scans by the others I have mentioned then you should be pretty safe.
Best of all they all have Free versions which are sufficent for a normal home user.