layouts/shortcodes/insertfile.html

{{$file := .Get "file" | printf "source/stories/%s"}}
{{- if eq (.Get "markdown") "true" -}}
{{- $file  | readFile | markdownify -}}
{{- else if  (.Get "highlight") -}}
{{-  highlight ($file  | readFile) (.Get "highlight") "" -}}
{{- else -}}
{{ $file  | readFile | safeHTML }}
{{- end -}}