//Define full path to save
string pathString = @"c:\Top-Level Folder\SubFolder2";
string suffix = ".jpg";
string dateAsString = $"{DateTime.Now.Day}_{DateTime.Now.Month}_{DateTime.Now.Year}.{suffix}";

//Combine full path with filename
string fullPathString = System.IO.Path.Combine(pathString, dateAsString);
 
//Save
//Will overwrite the file if it already exists.
pbOrjinalImage.Image.Save(fullPathString, System.Drawing.Imaging.ImageFormat.Jpeg);