add support for archive files.

src/documents/models.py

@@ -224,6 +224,19 @@ class Document(models.Model):
     def source_file(self):
         return open(self.source_path, "rb")
 
+    @property
+    def archive_path(self):
+        fname = "{:07}{}".format(self.pk, ".pdf")
+
+        return os.path.join(
+            settings.ARCHIVE_DIR,
+            fname
+        )
+
+    @property
+    def archive_file(self):
+        return open(self.archive_path, "rb")
+
     @property
     def file_name(self):
         return slugify(str(self)) + self.file_type