Crop pdf removing content cropped away

I do have a pdf that contains a drawing, a part of which I would like to extract. I am able to open the pdf in inkscape. However, it contains a group with 150k items. As far as I see, there are no subgroups that I could select as entity. Now just trying to select the parts that I would like to delete does not work (inkscape still has 100% CPU load after 3 hours). Is there a command line tool that would allow me to crop the pdf *and* to delete the elements that are outside the cropped area? This would then allow me to further edit the extracted section using inkscape.