Some people take SumatraPDF's code, rename it, bundle additional crappy software and distribute it.
RocketPDF is one of those programs. It's a Sumatra rip-off and you shouldn't be using it.
We, the SumatraPDF developers, do all the hard, on-going work behind the app.
We provide documentation.
We provide support.
The ripoff artists that use our work do none of those things.
All you get is questionable software installed on your computer alongside the app that is merely renamed SumatraPDF.
Unless you want your computer to be infested with malware, unwanted browser toolbars etc., use the original SumatraPDF, downloaded from our official website.
As an additional slap in the face, they have the gall to ask for donations, so that you can give them money for the code that I wrote.