GIMP :: Degradation Of Image After Extracted From PDF - Pixelation Of Lines

Basically, I am trying to process a simple drawn map that was scanned and saved as a PDF. The scanned image is old so the paper is yellowed and they scanned it in high res color even though the image is black and white (well, blue ink actually). I just want to make the background white and change the blue/black lines to solid black lines that retain their clarity.

Here is a portion of the image:

The left is the original and the right is what I WANT, but cannot, achieve.

My biggest issue has been pixelation of the lines. I just can't get it smooth like in the right image. I've tried all sorts of filters - blurs, smooths, sharpens etc.. Part of the problem is also the degradation of the image after I extract it from the PDF.