edit pdf's

[Matt Price <matt@derailleur.org>]

hey folks,

I have a bunch of pdf's I'd like to print out, scanned from
small-paged books.  I'd like to print them out two-to-a-page, but
they've been saved with lots of blank space around the text; so when I
just try

lpr -o number-up=2

I get very  very tiny type.  I'd like to somehow strip the blank space
away from the original files... but I have no idea whether it's
posswible to do that in, say, a text editor, by editing some of the
readable text.  Anyone have any other idea how it might be done?  Is
there a program lurking out there that might work (apt-cache didn't
seem to find anything).  

thanks much,
m