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Hi. This is created as suggested from evince issue 446.

Evince is unable to open PDFs encrypted with 256 bit AES (AESv3) encryption.

I'm seeing this problem with evince 3.30.2 running on Ubuntu (disco).

1. Show some info on qpdf and evince versions.

   $ dpkg-query --show evince
   evince	3.30.2-1
   
   $ evince --version
   GNOME Document Viewer 3.30.2
   
   $ qpdf --version
   qpdf version 8.2.1

2. Download a PDF to work with.

    $ wget https://www.adobe.com/support/products/enterprise/knowledgecenter/media/c4611_sample_explain.pdf -q -O plain.pdf
    $ md5sum plain.pdf 
    88bb00da1e9bab21e9cb13248b8770b1  plain.pdf

3. Encrypt it using qpdf and AES 256.

    $ rm -f encrypted-256.pdf encrypted-128.pdf
    $ qpdf --encrypt user-secret owner-secret 256 -- plain.pdf encrypted-256.pdf
   
    $ egrep -a AES encrypted-256.pdf
    << /CF << /StdCF << /AuthEvent /DocOpen /CFM /AESV3 /Length 32 >> >> /Filter /Standard /Length 256 /O <a868eeb995f6ff82543b1f38ab35f99cd9fd3611ddcfbb93f845b895fe64633fbf4e2714dd4dae142ccb602a50ede355> /OE <95e714077d596a65fecf766c94144c09341c9ddedc6f4237852960de7fc6d417> /P -4 /Perms <f708e990e02ae1ddc85b5a120731edc1> /R 6 /StmF /StdCF /StrF /StdCF /U <f972aa5c9877fd6d6650ca7b2705e12141f9d9d711a3378cd5e51c77c5dbc291e5270b54a36015d38b111c1c562a0749> /UE <435b9bd03432ad84261eb3bf19e00ce236e3acc26d831359fa8d2bacf758d1d0> /V 5 >>
   
   
    $ qpdf --password=user-secret --show-encryption encrypted-256.pdf
    R = 6
    P = -4
    User password = user-secret
    extract for accessibility: allowed
    extract for any purpose: allowed
    print low resolution: allowed
    print high resolution: allowed
    modify document assembly: allowed
    modify forms: allowed
    modify annotations: allowed
    modify other: allowed
    modify anything: allowed
    stream encryption method: AESv3
    string encryption method: AESv3
    file encryption method: AESv3

4. Attempt to view with evince. supplying either user or owner password does not work.

5. For comparision, try with AES 128 bit.. evince works fine here.

    $ qpdf --encrypt user-secret owner-secret 128 --use-aes=y -- plain.pdf encrypted-128.pdf
   
    $ qpdf --password=owner-secret --show-encryption encrypted-128.pdf
    R = 4
    P = -4
    User password = user-secret
    extract for accessibility: allowed
    extract for any purpose: allowed
    print low resolution: allowed
    print high resolution: allowed
    modify document assembly: allowed
    modify forms: allowed
    modify annotations: allowed
    modify other: allowed
    modify anything: allowed
    stream encryption method: AESv2
    string encryption method: AESv2
    file encryption method: AESv2