Hi,
The help.pdf is a readonly file ,it can not modified.
Did you use iTunes move file to PDFViewer Document?
set break point at RDFileTableController line 133,check if path like
/var/mobile/Containers/Data/Application/874CE321-6B3A-4122-B068-65CBB12574D8/Documents/
If in this document,check if your device has writable authority, write a file write demo ,
use
fopen( sFile, "rb+" );
then write something to check.