A project file and a review document serve different roles
CDR is an editable design document that can preserve objects, layers, and application-specific details. PDF is easier to circulate for comments and may keep page appearance stable, but it is not a replacement for the full authoring project.
Keep the CDR master when future edits are expected. Treat the PDF as a handoff copy, and identify its revision so reviewers do not mistake an older export for the current artwork.