diff -r 45cd55248ffd -r 7af210f1f13b src/Pure/Thy/sessions.scala
--- a/src/Pure/Thy/sessions.scala	Mon Nov 23 16:18:22 2020 +0100
+++ b/src/Pure/Thy/sessions.scala	Tue Nov 24 16:39:58 2020 +0100
@@ -1211,7 +1211,7 @@
       read_export(session, theory_name, name) getOrElse
         Export.empty_entry(session, theory_name, name)
 
-    def read_document(session_name: String, name: String): Option[Presentation.Document_PDF] =
+    def read_document(session_name: String, name: String): Option[Presentation.Document_Output] =
       database_server match {
         case Some(db) => Presentation.read_document(db, session_name, name)
         case None =>