No problem man, everything ok.
PDF format sucks because it has fixed format, is like a picture, so depending the size of your reading device you could end up with extremely small text that's unreadable, besides is an extremely closed format, readers other than Adobe's ones don't fully support the format, and also there are know security vulnerabilities in PDFs that can compromise your computer because it supports a scripting language.
New ebook formats like mobi/epub are dynamic, the text is saved like in an HTML webpage, so the paragraph adapts to your device width, and you can change font size.
To read mobi/epubs you can use Calibre also, it supports all kind of formats and its the program I used to create the compilation, its use is kind of complicated, but in its installation directory there is an executable called "ebook-viewer.exe" using that you can open the ebook without worrying about the libraries and all that crap.
Calibre is free and you can get it from
http://calibre-ebook.com/downloadMaybe with the free amazon Kindle reader for PC you can also read the .mobi