Pdf Expert is great but I believe on the iOS, Apple will not allow javascript to run from within a document, which certain form functions such as a "submit form" button require.
http://blog.epdoc.com/2010/05/ipad-spells-end-of-document-innovation.html
"3.3.2 An Application may not itself install or launch other executable code by any means, including without limitation through the use of a plug-in architecture, calling other frameworks, other APIs or otherwise. No interpreted code may be downloaded and used in an Application except for code that is interpreted and run by Apple’s Published APIs and built-in interpreter(s).
In fact the rules are even more stringent because the only built-in interpreter is Javascript, and it is only available from within Webkit, and you can't use it to manipulate your own document object model (DOM). Meaning the only content you are allowed to script is HTML. That means other interactive document formats are just plain verbotten.
There are some pretty reasonable and popular document formats out there that are not HTML. PDF and Excel spreadsheets are but two examples. PDF actually supports interactivity in several ways, including embedding Javascript (a basic use is to do the math in PDF forms) and 3D. The forms Javascript is an older variation that is not compatible with the Apple-provided interpreter (you can't really update 10 year old documents nor call Adobe lazy for not doing so). Even if it were, the Javascript has to bind to a native DOM, and Apple's Javascipt interpreter does not allow this.
Apple Preview supports a subset of PDF but does not support embedded Javascript. Rule 3.3.2 forbids an application from supporting PDF with Javascript. This is really too bad, because I could have seen the iPad as being a great, portable platform for using PDFs with rich forms entry and calculations."
This is really too bad
