PDFtk is a toolkit for manipulating Portable Document Format documents. It runs on Linux, Windows and MacOS. It comes in three versions: PDFtk Server, PDFtk Free and PDFtk Pro. It is able to concatenate, shuffle, split and rotate PDF files. It can also show and update metadata .

How to Install ?
i search in google but no luck also in pdftk official document don’t have instruction for centos 7 🙁  so here is solution for public

Step 1 : Login Your Server / VPN

Step 2: Open Terminal
Step 3 :  Now  Copy & Past this Code

    copy robert-gcj-epel-7.repo to /etc/yum.repos.d folder

wget https://copr.fedorainfracloud.org/coprs/robert/gcj/repo/epel-7/robert-gcj-epel-7.repo -P /etc/yum.repos.d

robert-pdftk-epel-7.repo to /etc/yum.repos.d folder

wget https://copr.fedorainfracloud.org/coprs/robert/pdftk/repo/epel-7/robert-pdftk-epel-7.repo -P /etc/yum.repos.d

yum install pdftk

Before run all First Check link active or not 

ping copr.fedorainfracloud.org

Have a Good Day !!!