How can I convert a jpg doc into word document to do modifications

A JPG image cannot be directly or easilly imported into Microsoft Word.

One option would be to use software that does Character Recognition to try and extract text from the image. You will loose most of the formatting and it is likely to have characters that are not properly identified, so it would need a lot of fixing.

Some scanner software will do Optical Character Recognition, so you might be able to print the image and re-scan it to have the text recognized. If you have access to the full version of Adobe Acrobat, you could also import the image and use the text recognition tools there.

There is other third party software that can do this, although I'm not sure how well and the costs vary (for example: Image to OCR Converter).

If it's not too big of a document, you're porbably better off re-creating it directly in Word.

I have used this site it is a OCR engine. Like any OCR tyou need to check the results there may be mistakes but usually it works well.