According to cupsd.conf(5), the default setting for PreserveJobFiles is 86400, so printed documents are only preserved for 24 hours. Paranoid users can set this

According to cupsd.conf(5), the default setting for PreserveJobFiles is 86400, so printed documents are only preserved for 24 hours. Paranoid users can set this to "no" to cause them to be removed immediately after printing. I'm skeptical of the claim that that job files are preserved "forever" unless CUPS has been configured thus.