Problem with Horizontal line exceeding page margins

Hello everyone,

I am having a problem drawing a simple horizontal line. All I'd like is a
slim horizontal line that goes from left margin to right margin.

Here is the relevant code:

def @HLine
  left size
{
@BackEnd @Case {
  PDF @Yield {
    { 0 0 m __xsize 0 l __mul(size, __pt) w S } @Graphic {}
  }
}
}

As you can see I am using the PDF back-end.

When I look at the PDF in Adobe Acrobat, it looks fine. However, when I
print the document, the right end of the horizontal line exceeds the right
margin, by a significant amount, around half an inch.

Anyone have any ideas? I know the PDF's graphic capabilities are inferior
to PostScript, but I have to use PDF. Hopefully as something as simple as a
basic horizontal line is possible.

Regards,
Michael Koehmstedt