See http://www.tgm.vn/ebook/?e=NDc9NTA1JmJvb2s9VG9pVGFpR2lvaUJhbkN1bmdUaGUtZWJvb2stMi4wLnBkZiY2MTM0PTM0NTA1 for a (large) document which MuPDF can't open due to it not yet supporting the encryption algorithm introduced with Adobe Reader 9.
Created attachment 7207 [details] add SHA-256 and support for encryption revision 5 to MuPDF
Thanks!