use signed uuid in previews

app/controllers/preview_document_page_controller.rb

@@ -6,7 +6,16 @@ class PreviewDocumentPageController < ActionController::API
   FORMAT = Templates::ProcessDocument::FORMAT
 
   def show
-    attachment = ActiveStorage::Attachment.find_by(uuid: params[:attachment_uuid])
+    attachment_uuid = ApplicationRecord.signed_id_verifier.verified(params[:signed_uuid])
+
+    attachment =
+      if attachment_uuid
+        ActiveStorage::Attachment.find_by(uuid: attachment_uuid)
+      else
+        Rollbar.warning("Load preview from uuid: #{params[:signed_uuid].to_s.first(10)}") if defined?(Rollbar)
+
+        ActiveStorage::Attachment.find_by(uuid: params[:signed_uuid])
+      end
 
     return head :not_found unless attachment
 
@@ -21,9 +30,10 @@ class PreviewDocumentPageController < ActionController::API
         find_or_create_document_tempfile_path(attachment)
       end
 
-    io = Templates::ProcessDocument.generate_pdf_preview_from_file(attachment, file_path, params[:id].to_i)
+    preview_image =
+      Templates::ProcessDocument.generate_pdf_preview_from_file(attachment, file_path, params[:id].to_i)
 
-    render plain: io.tap(&:rewind).read, content_type: 'image/jpeg'
+    redirect_to preview_image.url, allow_other_host: true
   end
 
   def find_or_create_document_tempfile_path(attachment)