White space when converting pdf to pdf?

[kim_earth]

(using imagemagick 6.20, ghost script 8.51 on a linux box.)

When converting several pdfs to one multipage pdf document, I'm getting the following:


My command is:
convert -density 300 -compress JPEG 20 hi1.pdf hi2.pdf hi.pdf

alot of whitespace and 2 tiny tiny images on seperate pages..
any other options I need?

thanks in advance..