This can be done using pdftk.

$ <in>pdftk form.pdf dump_data_fields > form_fields.txt</in>
$ <in>vim form_fields.txt</in>
[...]
$ # XXX generate data.fdf from form_fields.txt; see http://www.myown1.com/linux/pdf_formfill.shtml
$ <in>pdftk form.pdf fill_form data.fdf output data.pdf</in>

As adapted from here. PoDoFo.

$ <in>podofopdfinfo P in.pdf  | grep MediaBox</in>
        MediaBox: [ 0.000000 0.000000 841.680000 595.080000 ]
$ <in>podofobox in.pdf cropped.pdf crop 42050.0000 000.0000 84168.0000 59508.0000</in> # Note: dimensions are in centi-pts; and the coordinates start from the bottom-right

$ <in>gs -o cropped.pdf -sDEVICE=pdfwrite -c "[/CropBox [0 0 280.59 419.52] /PAGES pdfmark" -f input.pdf</in>

The unit of 'CropBox' (and 'MediaBox') are expressed in an unclear (to me) unit. In this example, 280.59 was 99mm.

Using Ghostscript unfortunately scrapes the metadata.

Once again, PDFTK comes to the rescue.

$ <in>pdftk input.pdf dump_data  | pdftk cropped.pdf update_info - output cropped2.pdf</in>

For example, 2xA5 on one A4 page. As seen here, this requires a Perl script.

split_pdf_A4_to_A5.pl

#!/usr/bin/env perl
# Original found at [0]
# [0] http://fitzcarraldoblog.wordpress.com/2013/11/09/split-an-a4-pdf-file-into-two-a5-pdf-files/
use strict; use warnings;
use PDF::API2;
 
my $filename = shift || 'test.pdf';
my $oldpdf = PDF::API2->open($filename);
my $newpdf = PDF::API2->new;
 
for my $page_nb (1..$oldpdf->pages) {
	my ($page, @cropdata);
 
	$page = $newpdf->importpage($oldpdf, $page_nb);
	@cropdata = $page->get_mediabox;
	$cropdata[2] /= 2;
	$page->cropbox(@cropdata);
	$page->trimbox(@cropdata);
	$page->mediabox(@cropdata);
 
	$page = $newpdf->importpage($oldpdf, $page_nb);
	@cropdata = $page->get_mediabox;
	$cropdata[0] = $cropdata[2] / 2;
	$page->cropbox(@cropdata);
	$page->trimbox(@cropdata);
	$page->mediabox(@cropdata);
}
 
(my $newfilename = $filename) =~ s/(.*)\.(\w+)$/$1.split.$2/;
$newpdf->saveas($newfilename);
 
__END__

This script is trivial to use.

$ <in>./split_pdf_A4_to_A5.pl in.pdf</in>

It will create a 'in.split.pdf' file.

Based on this.

$ <in>pdf2ps in.pdf a.ps</in>
$ <in>psbook a.ps b.ps</in>
$ <in>ps2pdf b.ps c.pdf</in>
$ <in>pdfnup c.pdf --nup 2x1</in>

The output is 'c-nup.pdf'.

As seen here.

This is trivial with pdftk and a blank page of the right size.

$ <in>pdftk A=in.pdf B=blank.pdf cat A1 B A2-end output out.pdf</in>

$ <in>echo "" | ps2pdf -sPAPERSIZE=a5 - blank.pdf</in>

Custom PAPERSIZE dimensions can hakishly be added to /usr/share/ghostscript/${GS_VER}/Resource/Init/gs_statd.ps