Photoshop PSD (and Photoshop EPS, and Photoshop PDF) are the only formats which support Duotone images (amongst other things).
I'm a bit disappointed since I was hoping to print our Annual Report using Duotones. I'm seeing if there's a way to translate the color channels of a duotone to arbitrary color channels in a CMYK file, then ask the printer to substitute the appropriate inks at press. (I'm using this approach for spot colors elsewhere in the document, specifying items with a Cyan ink value, and then instruct the printer to use a specific pantone color instead)
I'm a bit disappointed since I was hoping to print our Annual Report using Duotones. I'm seeing if there's a way to translate the color channels of a duotone to arbitrary color channels in a CMYK file, then ask the printer to substitute the appropriate inks at press. (I'm using this approach for spot colors elsewhere in the document, specifying items with a Cyan ink value, and then instruct the printer to use a specific pantone color instead)