Maybe I am wrong, but in my opinion, installing one package from CentOS 6 which is deprecated and no longer shipped in CentOS 7, will do no harm to the system at all. The only problem that could come into play in this concrete situation is that pdftk will not work properly.TrevorH wrote:This is a recipe for disaster: you should not install CentOS 6 packages on CentOS 7.
But I aggre that in general installing packages from previous version can mess up the system.