Acrobat Javascript Crop Scanned Pages

I need someone to be able to write a javascript function that will be listed under the "Document" heading in acrobat and it will crop the bottom 3 inches of the document. The javascript should detect the page size, and crop the bottom so that the entire page is 8.5 x 11. It should do this for every page in the document. I do not always know how many pages will be in each document I need to crop. Thanks