File size after split

I have a customer who send me rather big pdf-files (2 Gb+) and I need to perform color matching on these pdf files.

When I try to split the pdf into single pages in Enfocus Switch with the Adobe Acrobat Professional configurator Acrobat will crash. If I use Enfocus Split PDF configurator it will crash due to an time out error.

So I decided to try to split the pdf into several smaller files, however the file size remains the same regardless of whether the file contains one or 52 pages. If I save the pdf as a postscript file and then destill the postscript file the pdf with be about 5 Mb rather than the 311 Mb the original file is, but why is it that I have to go thru the postscript - destill steps in order to reduce the file size? It seems like Acrobat when splitting a pdf file keeps everything in the file, but disables viewing/output of the discarded pages until you select to create a postscript file. Then and only then Acrobat will trash everything not related to the page, hence reducing the file size of the destilled page.