diff --git a/src/img2pdf.py b/src/img2pdf.py
index 5e5a640..0bf0376 100755
--- a/src/img2pdf.py
+++ b/src/img2pdf.py
@@ -1070,12 +1070,7 @@ class pdfdoc(object):
                 if iccp is not None:
                     self.writer.addobj(iccpdict)
 
-    def tostring(self):
-        stream = BytesIO()
-        self.tostream(stream)
-        return stream.getvalue()
-
-    def tostream(self, outputstream=None, return_engine_doc=False):
+    def todoc(self):
         if self.engine == Engine.pikepdf:
             PdfArray = pikepdf.Array
             PdfDict = pikepdf.Dictionary
@@ -1267,12 +1262,16 @@ class pdfdoc(object):
                 self.writer.addobj(metadata)
                 self.writer.addobj(iccstream)
 
-        if return_engine_doc:
-            return self.writer, self.output_version
+        return self.writer, self.output_version
 
-        # now write out the PDF
-        if outputstream is None:
-            raise TypeError("pdfdoc.tostream() requires outputstream unless return_engine_doc is True.")
+    def tostring(self):
+        stream = BytesIO()
+        self.tostream(stream)
+        return stream.getvalue()
+
+    def tostream(self, outputstream):
+        # write out the PDF
+        self.todoc()  # finalize self.writer
         if self.engine == Engine.pikepdf:
             kwargs = {}
             if pikepdf.__version__ >= "6.2.0":
@@ -1281,6 +1280,7 @@ class pdfdoc(object):
                 outputstream, min_version=self.output_version, linearize=True, **kwargs
             )
         elif self.engine == Engine.pdfrw:
+            from pdfrw import PdfName, PdfArray
             self.writer.trailer.Info = self.writer.docinfo
             # setting the version attribute of the pdfrw PdfWriter object will
             # influence the behaviour of the write() function
@@ -2803,11 +2803,11 @@ def convert(*images, **kwargs):
             )
 
     if kwargs["outputstream"]:
-        pdf.tostream(outputstream=kwargs["outputstream"])
+        pdf.tostream(kwargs["outputstream"])
         return
 
     if kwargs["return_engine_doc"]:
-        return pdf.tostream(return_engine_doc=True)
+        return pdf.todoc()
 
     return pdf.tostring()