That depends on how the original PDF is created and what is the content inside
PDF is a view format and the word 'and' might be stored as the word and, three seperate glyphs a,n,d or it may be a set of curves that look like and to you but is really just a set of curves.
Or it could be a form with fields in it containing data.
For most of the above you need to work with some plug-in or other, posting a demo woudl be the best way to get some specific help.
I've used Scribe from 360 Works it works great and is easy to use. The PDF's have to be PDF forms in order for it to work. Contact me at firstname.lastname@example.org if you want more details about my experience with it or have more questions.