I think the problem is Canva itself! It is informal and design-heavy but totally inappropriate for anything that needs to be accurately printed.
All content in a Canva document is RGB with absolutely no color management, i.e. DeviceRGB. There is no concept of gray or CMYK or any flavour.
When you download a “print” PDF file, all content is DeviceRGB. Black is DeviceRGB=(0,0,0) and white is DeviceRGB=(255,255,255). To make matters worse, even a “blank” page has an edge to edge color of DeviceRGB=(0,0,0). (You can confirm this with the Object Inspector tool within Output Preview in Adobe Acrobat Pro. That is probably where the problem is. Your RIP / DFE is making some assumption as to what colorspace the DeviceRGB really is, perhaps sRGB? And it is converting sRGB to whatever CMYK profile you are assuming, such as SWOP. In such a conversion, RGB=(255,255,255) does not necessarily convert to CMYK=(0,0,0,0).
There are two solutions possible here, both kludgy:
(1) Use the edit tools in Acrobat to totally remove the RGB “white” background object if that is the only “white” that you are dealing with.
(2) Use Acrobat Preflight to convert any vector or text RGB=(0,0,0) to Gray=(0) or CMYK=(0,0,0,1) and RGB=(255,255,255) to Gray=(1). You may need to create a custom fixup (as I have personally done in the past for this). This would also convert rich blacks to pure black (i.e., K-only).
Good luck. Note that neither Canva nor the newly released Adobe Create Cloud Express software are really setup for any serious printing but rather, for amateur-hour, quick and dirty designs for those who really aren't particular about output quality. This may change in the future, but for the time being, print service providers would be best advised to caution customers away from these “cheap” but problematic design tools.
- Dov
