Add error handling for invalid pdfs

scripts/pdf_unlock.py

@@ -76,14 +76,21 @@ def isencrypted(pdf_name):
 
     Returns:
         True if encrypted, otherwise False
+        
+    Raises:
+        AttributeError if pdf info cannot be obtained
     """
-    pdf_info = pdfinfo(pdf_name)
-    status = pdf_info['Encrypted'].split(' ')[0]
-
-    if status == 'yes':
-        return True
-    else:
-        return False
+    try:
+        pdf_info = pdfinfo(pdf_name)
+        status = pdf_info['Encrypted'].split(' ')[0]
+        if status == 'yes':
+            return True
+        elif status == 'no':
+            return False
+        else:
+            raise ValueError
+    except (SyntaxError, KeyError, ValueError):
+        raise AttributeError('Could not read pdf info.')
 
 
 def pdf_unlock(pdf_file, overwrite=False):