sudo dpkg -i libmng1_1.0.10-3_amd64.deb
sudo dpkg -i libqt3-mt_3.3.8-b-8ubuntu3_amd64.deb
sudo dpkg -i pdfedit_0.4.5-2_amd64.deb
Note: It worked on Ubuntu 14.04.5 LTS, evenif pdfedit sometimes crashes...
The program pdfedit seems to be few (or not) maintained nowadays.
One (hard) way should be to pass through the source code, following the path given by the site you will finish to the sourgeforce repository, always useful to take the code, but not updated almost 7 years (from 2010-05-11).
Downloading the source code,
./configure will probably throw you the error
configure: error: QTDIR environment variable must Be Set
and you will finish before or after to incur in the need to install
qt3 and specifically
libqt3-mt. Note that
So you can as suggested by another answer the old repositories
deb http://old-releases.ubuntu.com/ubuntu lucid main
or you can use the fast solution since even the support for the
libmng1 libraries are dropped.