Comment 7 for bug 524517

PDF's objective is to reflect the exact appearance of text. For Hebrew, it means that the glyphs are stored in visual order. If your PDF viewer accepts user input in logical order (which is the case in Windows and Linux), it should transform search arguments (captured from a user dialog) from logical to visual order before performing the search.
For Arabic, there is the additional issue that the glyphs represent letter shapes, and you must perform "shaping", in addition to reordering, on the search arguments to choose the proper glyphs for each Arabic letter.