Humbled by a Bundle

I just downloaded a Humble Bundle, only to be told I have no way to open those files. Apparently they all end in .mobi. I have no idea what that is. Do I really have to get another app to deal with this?

 

That's cool. I checked out the instructions (ha ha) and found that mobi is for that amazon thing, no wonder. I figured epub would do it, but no. Finally I just went with pdf and that worked, thank goodness. I should probably look at more of those bundles.

 

Here we go again. This time it's not a bundle but a pdf. It's listed in Files but I don't have an app to open it. Perhaps these photos will help.

 

I got that problem solved. Now I have to figure out whether it's better to go with pdf or epub if I have a choice. Is it possible to translate mobi? Why are some files mb while others are kb, and why are there sometimes differences in size between different versions?

 

I found a couple interesting titles but they are both in djvu, with no apparent way to translate. I guess Nook can't handle that. There is a Sumatra reader but it seems to be windows only. By the way, I have a new problem, yay. I was looking at a "book" and the pages disappeared. I could make them reappear but they vanished again, and fast. I have no idea how to fix that. It's happened with two of them.

 

One file I downloaded has huge gaps. There are some blank pages and others with just a little at the top. Is there any way to "tighten it up" and make it more compact?

 

Yeah, I just found out about that. It's probably best to get files in epub if it's available. Apparently some of the problem was having pdf converted to that format. I guess it's ok if it works but sometimes it doesn't. I went back and got some of the troublesome items in pdf instead as I probably should have in the first place. Leave well enough alone is a good motto.