resize page

i want to resize a page not by scaling it but resising to custom size

and to resize all the objects in it at the same time, keeping the aspect ratio

is this possible?

You can use pdftron.PDF.Page.Scale(fract) to rescake the page
(including all contents on the page). After (or prior to) scaling you
can also adjust the page dimensions using page.SetCropBox(bbox)/
page.SetMediaBox(bbox) (e.g. as shown in RectTest sample project -