diff -ura signpdf-0.0.3.orig/signpdf.py signpdf-0.0.3.new/signpdf.py
--- signpdf-0.0.3.orig/signpdf.py	2015-04-25 19:13:15.000000000 +0100
+++ signpdf-0.0.3.new/signpdf.py	2018-11-01 19:11:00.941260261 +0000
@@ -44,7 +44,7 @@
             # Create PDF for signature
             sig_tmp_filename = _get_tmp_filename()
             c = canvas.Canvas(sig_tmp_filename, pagesize=page.cropBox)
-            c.drawImage(args.signature, x1, y1, width, height)
+            c.drawImage(args.signature, x1, y1, width, height, mask='auto')
             if args.date:
                 c.drawString(x1 + width, y1, datetime.datetime.now().strftime("%Y-%m-%d"))
             c.showPage()
@@ -59,7 +59,7 @@
 
         writer.addPage(page)
 
-    with open(output_filename, 'w') as fh:
+    with open(output_filename, 'wb') as fh:
         writer.write(fh)
 
     for handle in [pdf_fh, sig_tmp_fh]: