GoodReader is a very versatile app. Not only does it give you the ability to read PDF and other large TXT files, it handles them quickly. If you are looking to mark up the PDF with your own notes, you can do that too. Besides being about to read just about all the popular text formats like, iWork, MS Office .doc, .ppt, .xls, you can also read HTML and Safari webarchives, high rez images, and audio and video files. This app also allows to manage and sync your files and folders of files with Dropbox, SkyDrive, SugarSync and any webDAV, AFP, SMB, FTP or SFTP server. All disguised as a little PDF reading app.
Go get it at the App Store: https://itunes.apple.com/us/app/goodreader-for-ipad/id363448914?mt=8
Visit the creator’s website and find out more about it: http://www.goodreader.com