You cannot do so - the browser will not allow this because of security concerns. Although there are workarounds, the fact is that you shouldn't count on this working. The following Stack Overflow questions are relevant here:
In addition to these, the new HTML5 specification states that browsers will need to feed a Windows compatible fakepath into the input type="file"
field, ostensibly for backward compatibility reasons.
So trying to obtain the path is worse then useless in newer browsers - you'll actually get a fake one instead.