Add option to decrypt PDFs during conversion

Refs: #1074

modules/joex/src/main/resources/reference.conf

@@ -586,6 +586,21 @@ Docpell Update Check
       }
       working-dir = ${java.io.tmpdir}"/docspell-convert"
     }
+
+    # Allows to try to decrypt a PDF with encryption or protection. If
+    # enabled, a PDFs encryption or protection will be removed during
+    # conversion.
+    #
+    # For encrypted PDFs, this is necessary to be processed, because
+    # docspell needs to read it. It also requires to specify a
+    # password here. All passwords are tried when reading a PDF.
+    #
+    # This is enabled by default, using an empty password list. This
+    # removes protection from PDFs, which is better for processing.
+    decrypt-pdf = {
+      enabled = true
+      passwords = []
+    }
   }
 
   # The same section is also present in the rest-server config. It is