First, the core PDF specification needs to be understood. Portable Document Format (PDF) documents were designed to run on many different desktop computers. A PDF document is "distilled" from different types of components. There are a few basics types of objects and that is where the differences from image file formats like JPG or TIFF start. PDF documents have headers, which are very small and contain only rudimentary information. The second part is the body which contains objects. Objects are numbered and can be of many types themselves. There are cross references and then the trailer. Besides these, the types of things you might find inside a PDF document are fonts, XMP metadata, a signature dictionary, the PDF envelope, attachments, annotations, embedded files such as images and more.
Now Adobe and others have done a good job of rendering normal PDF's on mobile, but forms, especially flowable, multi-page PDF forms, present some huge challenges. With soft keyboards (the popup keyboards on popular smart phones for example), the rest of the document must ensure that the form fields are not covered when then user is typing.
So what do you going to do if you have made a huge investment into something like Adobe LiveCycle ES for forms based business processes and now have to support mobile devices? Technoracle has a solution for this today. You also can re-write your forms from scratch (costly) or build custom native applications for each platform.