There are a number of PDF Music Readers for the iPad on the App Store, but the two PDF Music Readers on the App Store have some news that you should be aware of.
First, forScore released its latest version of its app today, and it graphically follows the styling cues of iOS 7 with its color scheme and fonts. There are a bunch of other improvements, including multiple libraries (for multiple users of one iPad), using multiple audio files with one score, collaboration (control of multiple devices), tagging options and a web-based metadata editor, dealing with embedded annotation in PDFs, and more. If you don’t have forScore, it is a must-have for any musician, and can be purchased here (referral link). If you have forScore, download the free update.
unrealBook for iPad (referral link) is another major player in the category of PDF Music Readers for the iPad, which has some unique functions that are not available on forScore, such as the ability to control some MIDI commands and to record audio while using the app (these are not the only tools). Unrealbook has been around since the early days of the iPad in 2010, and has been steadily adding features. I recommend owning both forScore and unrealBook–it is always a good idea to have a backup app in case something happens with your “normal” app. The developer of unrealBook recently created unrealBook Mobile, a version of unrealBook that runs on your phone. It also interacts with the iPad app. If you have unrealBook, you should consider the extra benefits of unrealBook Mobile. You can purchase unrealBook mobile here (referral link).