PRTD is only for those who have been granted Permanent Residence but do not yet have a PR card.
A refugee travel document is issued upon request to all Convention refugees in lieu of their national passport whether they are a PR or not.
To travel outside Canada as a Convention refugee you need an RTD. You do not need a PRTD if you have an RTD.
Whether you need a Schengen visa depends on your country of destination, since some Member States waive this requirement for refugees recognized in Canada while others don't. Here's a a sheet to see whether a Member State derogation applies to your or not: exceptions to the visa requirements
