program has picked up about 100 duplicate files

CCleaner for Windows
1

Question. What happens if I select them all? Or should just save the just one?

duplicate.txt

2

I'd suggest taking a look at this article: https://support.piriform.com/hc/en-us/articles/204950144-How-do-I-use-CCleaner-for-Windows-Duplicate-File-Finder- (specifically, the Which duplicates should I delete? section).

In short, though, please do not delete any files from the Windows, Windows.old, or Program Files (or Program Files (x86)) folders - I see several of these listed in the list.

Files in your Download folders, or libraries such as your Documents, Pictures, or Videos libraries should be fine to delete as long as you're sure you no longer want them. For other folders, though, I'd recommend a great deal of caution.

3
53 minutes ago, johnccleaner said: 
<div class="ipsQuote_contents ipsClearfix" data-gramm="false">
	<p>
		as long as you're sure you no longer want them.
	</p>
</div>

pay close attention to this part of john's post.