Readdle makes several highly rated "productivity" iOS apps, including Readdle Docs, Scanner Pro, Printer Pro, and PDF Expert. They tend to run a little pricier than your typical 99-cent game, ranging in price from about $4.99 to $9.99, which is why we thought it worth pointing out that Readdle is having a 48-hour sale to celebrate its 4th birthday (it rarely puts its apps on sale).
The developer is also behind the free Shakespeare app that gives you access to the complete works of William Shakespeare. A Pro version that adds features such as a glossary, scene breakdowns, and the ability to shake your device to display a random Shakespeare quote, usually runs $9.99 but is on sale for $6.99. It's also a universal app.