All of the comic files are packed on .CBR and/or .CBZ file formats and some comics are PDF, mobi and epub. Here are some of the reader apps that i can recommend : YAC Reader (Win, OSX, Linux, iOS), ComicRack (Win, Android, iOS), CDisplayEx.
To extract any compressed files, I recommend using 7-Zip.
If you want to download a comic and have broken links or is corrupt file, please use Broken Links Reporter (very easy to use) and is located on every comic post down after download links. Use a real mail address if you want to know when is fixed a broken link. Thanks!