As you can see in the image below, the text on the picturebox is different from the one in the textbox. It is working alright if I use Graphics.DrawString() but
Seems you are providing wrong measure for font size in the first place and then adding extra thickness to the brush. Try this instead:
using (GraphicsPath path = new GraphicsPath())
{
path.AddString(
text,
_fontStyle.FontFamily,
(int)_fontStyle.Style,
e.Graphics.DpiY * fontSize / 72f, // em size
new Point(0, 0), // location where to draw text
string_format);
e.Graphics.SmoothingMode = SmoothingMode.AntiAlias;
e.Graphics.CompositingQuality = CompositingQuality.HighQuality;
e.Graphics.CompositingMode = CompositingMode.SourceOver;
e.Graphics.DrawPath(new Pen(Color.Red), path);
}