function SpotPlates: TPdfSpotPlateInfos;
| Result | TPdfSpotPlateInfos. Array of records with a zero-based Index and the separation Name as written in the file. Empty when the page uses process colours only. |
Spot colours are named separations printed with their own ink rather than mixed from process inks. Prepress review needs the list of names a page actually uses, which is what this returns
The Index field is what RenderSpotPlate takes, so a caller can enumerate the plates and rasterise each one
Native spot-plate enumeration is a capability of the loaded PDFium module. When it is missing the call raises EPdfError rather than reporting an empty list, so an empty result means "no spot colours" and not "cannot tell"