Hello,
You can create a new form control with a standard drop-down list control displaying all available templates and letting users to choose one of them. You can find some inspiration in Kentico
CMS Template selector (
~\CMSModules\PortalEngine\FormControls\PageTemplates\SelectPageTemplate.ascx.cs).
This control would need to return a
TemplateID of the selected template.
Then, you need to use the form control in a system attribute
DocumentPageTemplateID [Site manager -> Development -> Document types -> edit document type -> New System attribute -> Attribute name: DocumentPageTemplateID , Field type: <custom form control>]
Best regards,
Michal Legen