From 03f2f489cec0738d12038e5909dde3fba84f68db Mon Sep 17 00:00:00 2001
From: Ayke van Laethem <aykevanlaethem@gmail.com>
Date: Thu, 24 May 2018 13:02:10 +0200
Subject: [PATCH] pdf: Accept Identity encryption

Identity encryption means there is no encryption at all.
---
 read.go | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/read.go b/read.go
index 32a7c807..f788f0f2 100644
--- a/read.go
+++ b/read.go
@@ -896,6 +896,9 @@ func (r *Reader) initEncrypt(password string) error {
 	if V != 1 && V != 2 && (V != 4 || !okayV4(encrypt)) {
 		return fmt.Errorf("unsupported PDF: encryption version V=%d; %v", V, objfmt(encrypt))
 	}
+	if V == 4 && encrypt["StmF"].(name) == name("Identity") {
+		return nil // No encryption applied.
+	}
 
 	ids, ok := r.trailer["ID"].(array)
 	if !ok || len(ids) < 1 {
@@ -1003,6 +1006,9 @@ func okayV4(encrypt dict) bool {
 	if stmf != strf {
 		return false
 	}
+	if stmf == name("Identity") {
+		return true // No encryption applied.
+	}
 	cfparam, ok := cf[stmf].(dict)
 	if cfparam["AuthEvent"] != nil && cfparam["AuthEvent"] != name("DocOpen") {
 		return false