I often add lyrics (not documents) as textfile via copy and paste from Notepad (which comes with the iPad) or GoodReader.
The problem is that I can't edit neither the very first nor the very last two or three lines of the text. It scrolls up (upper lines) or down whenever the keyboard appears.
I help myself for the moment by adding a series of "return" at the very beginning and the end to avoid this scrolling away, but that way isn't satisfying for me.
I think all you need to do is scroll the page up or down so the top or bottom of the text field is visible. You can scroll the page by dragging outside of the text field.
Here are some additional tips for editing text on iOS: http://forum.arlomedia.com/index.php/topic,654.msg1558.html#msg1558
Simply scrolling didn't help, neither dragging within the lyrics field nor outside (following your advice). Though I can drag the bottom of the text up - in the moment I lift the fingertip the text scrolls back (like hanging on a rubber band)
But : Following your link portrait orientation does help. Now the whole text is editable.