Was it scanned to pdf or was it printed to pdf? If it was scanned then it's an image and you need to OCR it to convert it to text. If it was printed to pdf then there are converters you can use, or if you have the actual Adobe Acrobat (not reader) you can save it as Rich Text Format and open it directly in word. Hope this helps
The converter will only work if the file was converted to pdf from word or other text program, not if the file was scanned into the computer and then converted to pdf. If scanned the pages are actually images and would need to be OCR'd to convert back to text.
It is very simple use acrobat reader v.4 (old version). there is an option in tools menu. I have used it many times.