Okay - just realised that the last screen was just asking for a "title" for my question!
I have Adobe Acrobat XI standard, but would like to trial the "compare documents" feature on Pro. I tried to download a trial version of Pro, but the installer indicated that "it detected a more fully featured version of the product" - presumably my standard version? - and stopped installation. It is not clear to me what my options are for either upgrading to Pro, or selectively purchasing the "compare documents" plugin (if possible). I am using what is presumably an Enterprise version of acrobat (i.e. my employer owns it, not me) - so not sure what limitations that results in. I think this is a simple question, but would be grateful for advice.