> Doesn't the PDF on their site pretty much prove they can do both of these - at least, in a way? They were able to change the color without impacting the conte

> Doesn't the PDF on their site pretty much prove they can do both of these - at least, in a way? They were able to change the color without impacting the contents of the PDF and get the same SHA1. I think they prepared both PDFs and then tweaked with bits in both of them. This is much easier than tampering with only one PDF. So I think it's still very hard to generated a CA cert where you can just copy the signature of an existing cert. But maybe you can predict exactly what parts from your signing request and what timestamp and serial number and so on the CA will use, then you can maybe precompute a signing request that will result in a cert where you can replace some parts with other, evil, precomputed ones.