Hi @Anonymous,
This is where it would get tricky. The print command doesn't offer and invert colors option. In Adobe Reader, there is an option to invert the colors you can find it under Edit->Preferences->Accessibility->Replace Document Colors. The foreground and background colors that one wishes to be used can be specified here.
As I mentioned in my previous post and image is better suited for this type of process than a PDF. Here is the procedure I would recommend.
1. Open your board file
2. Click on the ULP icon on the top toolbar.
3. In the dialog that pops up double click cam2image.ulp
4. In then next dialog select gerb274x (this cam job is for 2 layer boards like yours)
5. In the next dialog, make sure to that the Monochrome option at the bottom is checked.
6. Set the DPI to 600 (Higher resolution will produce a thicker toner layer)
7.I would say leave the bitmap as the output format since it won't be compressed and will give you the purest result. Click OK
EAGLE will place the images in the same location as your board and schematic file. You are interested in the cmp(component side aka top) and sol (solder side aka bottom) files. If the colors are not what you want you can easily invert them in a program like MSPaint or GIMP.
You can see how other do it with this tutorial. A quick google search will pop up more ways to do this.
Let me know if there's anything else I can do for you.
Best Regards,

Jorge Garcia
Product Support Specialist for Fusion 360 and EAGLE
Kudos are much appreciated if the information I have shared is helpful to you and/or others.
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