Do you know the problem of having no more black ink in your printer - and a PDF document containing tickets or something else and in need of it printed?

This is a nice little hack - but you will need Photoshop.

1) Open the PDF in Photoshop - If 72 dpi is not enough you can change this to 300

2) Choose Image -> Mode -> Grayscale - Say Yes to discard color information

3) Choose Image -> Mode -> Duotone -> Click the color icon and choose the color that fits your remaining printer ink.

4) Now just print it or save it.

Hope this will save you from trouble at some point.