Interesting, I'm investigating the same issue in CF 2016, 9 YEARS LATER. So it's still a problem. Perhaps CF2021 will resolve it.
Since the underlying technology hasn't changed, you may probably encounter the same result.
When using CFDocument, we endeavored to ensure that 1) all images were local and 2) the image color palettes were Adobe-friendly. We also had to be very careful regarding which HTML, CSS and fonts were used. Small images were often duplicated even though each image was different. It was very frustrating and we almost lost a major client as a result.
After we switched to WKHTMLTOPDF for PDF generation (back when using CF8/9), we never encountered any of the same basic issues as we did with CFDocument. CFHTMLTOPDF is based on WKHTMLTOPDF, but we still prefer to use the non-blackboxed executable that we can upgrade at any time. (It also enables us to perform PDF generation concurrently as well as offline.)