Define a (custom) page size as desired.
Print the .pdf using said page size to a .ps file.
Distill to a pdf
Or use pdfcrop:
http://pdfcrop.sourceforge.net/
Or a script which uses pdftk:
#!/bin/bash
perl -pe "s/(Crop|Media)Box\s*\[(.+?)\]/\$1Box\[$2\]/g;" $1 | pdftk - output $3
(from
http://konrad.familie-kieling.de/com...x/63-crop-pdfs )