Print file has both color modes. how to solve this?

>and how to explain to client that his files should be in one mode?

They need not be in one color mode. They need to be prepared in the way the printing vender specfies. Which might be RGB or CMYK or even both, since that is possible when the vendor uses the APPE and allows PDF/X-4 to be sent to print. Vector parts such as small type and thin lines can be in CMYK for precise color values. Images or photorealistic vector art or stuff with blend modes can be in RGB for better conversion and brighter colors using the RIP.

You can still print rgb on a cmyk printer (and vice versa), but there may be color changes as the cmyk color gamut is smaller than the rgb one, so better to design for the output method as your colors will look closer to your design.

Completely depends on the printer and the RIP. Using device link profiles you could even convert RGB 000 to 100 K.

a 12 color inkjet printer will deliver far better results when you feed it RGB input.

 

When you save your pdf you should make sure the color profile you are choosing matches your print method.

The PDF should match what the print vendor specifies.

thank you, that was helpful.