convert multiple pdf color scan pic file into black and white with batch process with auto select all pic in pdf file

hi everyone

this is rana.

i have a million files of pdf color scan document  and i want to convert them into black and white to save the space.

i have already tried with (Action...automate and batch) thing.

in batch process i have two problem

1: photoshop only accept max 50 pdf file color scan pic and my every pdf file have more than 5 color document in each.

i want change this to 150 pdf file per batch proccess...50 pdf file is not enough.when i open more than 50 pdf file its say you have open too many file close window.

2:when photoshop accept  the 50 pdf file its show every file one by one and all color scan document pic in pdf file show and i have to select all the pic in one pdf file to convert into black and white......i have to do this step again and again with every pdf file till 50.then i start bath process .this is so much time cunsuming.

i only wanted that every color scan document in pdf file is auto select till 50 pdf file.

i d`not want repeat again and agian same step to select color document in every file.

3: also want photoshop auto deselect the blank page..

any solution for these 3 problem

help me