Thank you so much for taking time to read my message. Today I finally got it working!
I'm running Modx 1.0.5 and here is what I did:
There is this line in the snippet:
// Set the color of the header and footer line
$pdf->setLineColor(isset($lineColor) && (is_array(explode(',', $lineColor))) ? explode(',', $lineColor) : array(0, 0, 0));
which I commented out. I don't really understand why this line of code was making problem but I'm happy it works now.
Thank you for your guides Bob, they are very comprehensive for someone like me (I'm not a developer) and helped me so many times (added your page to favourites long time ago). I hope that modx team won't stop developing and improving it.
I've seen that in the newest release there is 'improvement to pageCache read logic', does this mean that the quirk that you wrote about on your website:
http://bobsguides.com/modx-cache.html
no longer exists?
JaneVi