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I'll take a stab. You can use a 301 redirect to enforce your canonical URL. In this case, it may be that site decided that /home.aspx is the canonical and wanted to be sure any links out there go to it. This is a strong signal to the search engine that if it has both www.domain.com and www.domain.com/home.aspx indexed, the /home is the URL for the juice.

Now, that assumes this was done on purpose and not just some silly mistake.

I've seen sites with 4 URLs for the main page:

www.domain.com

www.domain.com/home.aspx

domain.com

domain.com/home.aspx

You can read up on Google, but one way to fix this problem is to redirect 3 of the 4 to the canonical URL.

I don't think there's a problem with hosting the PDF. Just make sure you've got strong branding in the PDF and links back to your online article. People will most likely pass your PDF around to others and you want them to come visit the source --> YOU.

Google is clear they absolutely do not use meta keywords (see Matt Cutts video). If the keywords are spammy and useless, I'd clean it up. If the keywords are valid, I might consider removing them to make it harder on new competitors to figure out what this site owner thinks are valuable. End of the day, I agree that you could simply do nothing, but I tend to clean up and/or delete.