Open the color PDF in Photoshop.
Go to File and choose Open As and select RGB Color as the mode.
Once the PDF is open, go to Image and select Mode and then Grayscale.
This will convert the color PDF to grayscale.
To make the image truly black and white, go to Image and select Adjustments and then Black & White.
This will bring up a dialog box with various options for adjusting the grayscale image to achieve the desired black and white result.
Once you have made your adjustments, save the image as a new PDF by going to File and selecting Save As and choosing PDF as the file type.
It is important to note that when converting a color PDF to black and white using Photoshop, the resulting image may not be of the same quality as the original color PDF. Additionally, some information or details in the color PDF may be lost in the conversion process. Therefore, it is always recommended to keep a copy of the original color PDF for future reference.