Why not copy all the text in the PDF by using the Save As command, and then open in a wordprocessing program, use the find and replace function there, then re-PDF? Only of use of course if there are no graphics to worry about, as the process does not save the graphics as well.
From the Help files:
1 With the PDF file open, choose File > Save As.
2 In the Save As dialog box, select the location in which to save the file, choose Rich Text
Format from the Save as Type (Windows) or Show (Mac OS) menu, and enter a name for
the file in the filename text box.
3 Click Save.
4 Open the RTF file in your target application.
Note: Any images in the file are discarded.