On macOS BigSure, you can convert your color PDF files to grey color without any 3rd party or upload to any online services. Please do step inside this blog post.
Convert your PDF from color to grey scale
- Open your PDF file with Preview.
- Select menu File > Export…
- Select “format” to PDF and “Quartz Filter” to Gray Tone.
- Click “Save“.
That’s all. Enjoy your Mac. 😘