LibO 6.3 creates PDF v1.5, but LibO 6.4 help says it is v1.4

Is it possible to adjust PDF version in preferences, so LibO 6.3 actually exports to PDF v1.4, if necessary?

I don’t think that choosing older PDF version is possible. PDF 1.5 is there since 2003; it’s even older than 1.7 that became an ISO standard.

Please report outdated documentation issue to bug tracker. Thanks!