It depends on the format of pdf document. There are image type, text, and hybrid formats.
For a text type pdf, you can copy out the text and paste it into any application. To do this, turn on the text select tool on the Adobe Reader toolbar. It is the button that looks like a capital I or an i-beam. Once the text select tool is turned on, select and copy text just as you would in Word. Try this first in your pdf document.
If Adobe Reader will not let you select text, then the pdf document is in image format. You will need to convert the image to text. This can be done either with the OCR feature in Acrobat (not Adobe Reader) or a third party software.
If you have access to an OCR program, like Textbridge, and a scanner, you can print out a hard copy of the document, scan in the document into an image format that the OCR software can recognize, such as TIFF, and have the software convert that into a format that Word can recognize.