Convert color PDF to black grayscale.

Converting RGB CMYK color space to black gray color space.
When to use it?
If we wish to get single color gray tone PDF from the color (cmyk or rgb) PDF.
Monochrome PDF is now suitable for direct color printing such as monochrome pantone.
What part of PDF is affected by it?
The color spaces of images, fonts, graphical elements get modified.
The Pantone and separated colors of PDF are converted to single color PDF.
What to watch for?
This conversion affects the entire document, therefore, it is important to check the document after conversion.
How to use it?