I have a problem with the Gateway Pundit site anymore. As for this, we have to take his word or the word of the guy who twittered this originally, because the proof can not be opened to a size where the document is even readable.
That approach is pretty common among the 4-Chan and reddit "research" community so that they have a snapshot of a page recorded before they disclose the real URL, since often pages get changed or removed when the information becomes public.
Of course, visiting the URLs associated with that kind of research is best done from a computer with very strong anti-virus and malware protection.
Assuming no errors in the data on the cited web sites, there is evidence that a person voting in a number of elections by mail from the same home address as the protester died years before they voted.
I have also seen video which may show the same protester being escorted out of a Trump rally in Florida in August.