If I have pages from a book, so they're less than US letter size or A4, or whatever page size the scanner takes. But let's say they got scanned in as that page size the scanner takes. (Could be US letter size, could be could be A4 - the UK equivalent not exactly the same size but similar size)
How can I specify that I want to not necessarily rescale it to another size..(though that'd be good as a next after) but cut the excess white space off. For example
Ideally I want to do it for any arbitrary size. So I want to be able to specify sizes. As the page sizes may be A4 for the bigger one like what a UK printer takes, and A5 for the smaller book one. Or not A5. But the key is that I have PDFs of a bigger page size, and I want output that is the correct page size to match the page I placed onto the scanner for scanning.
And preferably i'd want to do this for free.
As an example, I want to turn this-