auto center and cropping of pdf file(s)

I have many pdf files which is created by scan from document. I need to center it, crop white margin, and resize it. So, this is what I need 1. select file(s) 2. select 'need to process pages', such as 3-20 (don't process cover page, and index page, for ex.) 3. resize ALL pages to A4 (need a check box, including/excluding ALL pages or only pages indicated before) 4. center content (set up even/odd pages seperately. Center the content or not. For ex., if page width is 100, content width is 80, the put it into center line (so left/right width margin is 10), or I can set it into 60/40, so left margin is 12, right margin is 8. Need to setup top/bottom height as well. (There should be noise tolerance. Because all documents are created by scan, so there are some noise on it. Treat small noice as white background.) 5. remove white margin propotional, and I can set up extra white margin. For ex., if the paper size is 20x20, content is 15x15, then resize the content to 20x20. If extra white margin is 2, the resize the content to 18x18. That's it. Note: 1. All process should be lossless. 2. Don't change color/dpi setting. In general, cover page is 300 dpi, color. Content might be 300 dpi gray, or 600 dpi black/white. 3. Auto backup. Therefore, I want that there is a config file, for ex., backup sub-folder name="done", the all processed files will be saved to xxxxx\done\processed file.pdf. And paper size, extra margin size, or any setting can be seen in this config file (pure txt). So running program is simple, import from file(s) or directory, and click run. In summery, all I need it, resize, center and resize again so the content can fit to paper size with extra which margin. Thank you for your help