Multipage pdf change page size

[stsogias]

Hello,

I have a huge amount of A4 multipage scanned pdf files, well organized in seperate folders.

I need to add a 40mm white strip to the bottom of each page in every file.

Is this possible?

I've tried to do it using an Action with Crop Page command with no success.

Every time I try to change the page size to a custom size (e.g. 8.278x13.000)



I use Acrobat XI Pro.