Okay, How to do this in Batch Mode. What about the file size. Can you please tell me how to do this in Batch Mode.
In Acrobat click "Tools" and select Actions or Actions Wizard or something like that (my Acrobat isn't an English version).
Select New Action and make the appropriate settings - as shown in my screenshot from Acrobat DC (older versions have the same tools but another appearance).
On youtube you can find some tutorials about actions in Acrobat too.
As I said above, I'm not an Acrobat evangelist. So if you've special questions about your task, please, ask the more experienced people in the Acrobat forum.