You can use AJAX & jquery to check if a file exists at particular path on your server.
$.ajax({
url:'http://www.example.com/somefile.ext',
type:'HEAD',
error: function()
{
//file not exists
},
success: function()
{
//file exists
}
});
Due to security reasons javascript can't directly access clients's file system. Maximum that yo can do is that you may have a browse button that allows user to browse and point to the file and then you can validate the file and perform the desired action. Otherwise try using java applets/flash.
Check Read a local file using JavaScript HTML5 file api (offline website)