As you probably don't want to pollute your production image with all dependencies pdftk requires - one way is to build pdftk somewhere else and deploy it to e.g. through S3.
Following is steps should get you started. Copy and paste from history so should show steps needed.
Pick up RedHat instance from AWS (or local Centos 6)
sudo su -
yum install gcc
yum install gcc-java
yum install gcc-c++
cd /tmp/
wget http://pkgs.repoforge.org/pdftk/pdftk-1.44-2.rf.src.rpm
rpm2cpio pdftk-1.44-2.rf.src.rpm | cpio -idmv
unzip pdftk-1.44-src.zip
cd pdftk-1.44-dist/
cd pdftk
make -f Makefile.Redhat
find / -iname libgcj.so.10.0.0
mkdir -p /tmp/pdftk
cp pdftk /tmp/pdftk
find / -iname libgcj.so.10.0.0
cp /usr/lib64/libgcj.so.10.0.0 /tmp/pdftk
cd /tmp/
tar cvzf pdftk.tar.gz pdftk
Make sure you copy tar package content in target machine (Linux AMI) as follows
libgcj.so.10.0.0 install to /usr/lib64
ls -alh /usr/lib64/libgcj.so.*
lrwxrwxrwx 1 root root 27 Sep 6 06:39 /usr/lib64/libgcj.so.10 -> /usr/lib64/libgcj.so.10.0.0
-rwxr-xr-x 1 root root 47M Sep 6 06:38 /usr/lib64/libgcj.so.10.0.0
I just used to S3 bucket to transfer file:
/usr/bin/s3cmd --force get s3://<your-bucket>/rpm/pdftk.tar.gz /tmp/
pushd /tmp
/bin/tar xzf pdftk.tar.gz
/bin/cp pdftk/pdftk /usr/bin/
/bin/cp pdftk/libgcj.so.10.0.0 /usr/lib64/libgcj.so.10.0.0
/bin/ln -s /usr/lib64/libgcj.so.10.0.0 /usr/lib64/libgcj.so.10.0
/sbin/ldconfig
popd