Unable to process signed document from Adobe Echosign

```
What steps will reproduce the problem?

See Attached file for test file.

$ pdfsh
Welcome to the PDF shell (Origami release 1.2.6) [OpenSSL: yes, JavaScript: no]

>>> PDF.read('Downloads/HWS-POA.pdf')
[info ] ...Reading header...
[info ] ...Parsing revision 1...
[info ] ...Parsing xref table...
[info ] ...Parsing trailer...
[info ] ...Propagating types...
[info ] Warning: This document contains encrypted data!
ArgumentError: data must not be empty
from /Library/Ruby/Gems/2.0.0/gems/origami-1.2.7/lib/origami/encryption.rb:789:in `update'
from /Library/Ruby/Gems/2.0.0/gems/origami-1.2.7/lib/origami/encryption.rb:789:in `decrypt'
from /Library/Ruby/Gems/2.0.0/gems/origami-1.2.7/lib/origami/encryption.rb:716:in `decrypt'
from /Library/Ruby/Gems/2.0.0/gems/origami-1.2.7/lib/origami/encryption.rb:485:in `decrypt!'
from /Library/Ruby/Gems/2.0.0/gems/origami-1.2.7/lib/origami/encryption.rb:176:in `block (2 levels) in decrypt'
from /Library/Ruby/Gems/2.0.0/gems/origami-1.2.7/lib/origami/encryption.rb:161:in `each'
from /Library/Ruby/Gems/2.0.0/gems/origami-1.2.7/lib/origami/encryption.rb:161:in `block in decrypt'
from /Library/Ruby/Gems/2.0.0/gems/origami-1.2.7/lib/origami/encryption.rb:154:in `each'
from /Library/Ruby/Gems/2.0.0/gems/origami-1.2.7/lib/origami/encryption.rb:154:in `decrypt'
from /Library/Ruby/Gems/2.0.0/gems/origami-1.2.7/lib/origami/parsers/pdf.rb:92:in `parse_finalize'
from /Library/Ruby/Gems/2.0.0/gems/origami-1.2.7/lib/origami/parsers/pdf/linear.rb:79:in `parse'
from /Library/Ruby/Gems/2.0.0/gems/origami-1.2.7/lib/origami/pdf.rb:123:in `read'
from (irb):1
from /Library/Ruby/Gems/2.0.0/gems/origami-1.2.7/bin/pdfsh:12:in `'
from /usr/bin/pdfsh:23:in `load'
from /usr/bin/pdfsh:23:in `'

What is the expected output? What do you see instead?

I'm able to open the file

What version of the product are you using? On what operating system?

OS X Yosemite
Origami 1.2.7
Ruby 2.0.0p481

```

Original issue reported on code.google.com by `jameshig...@gmail.com` on 21 Dec 2014 at 7:34

Attachments:
- [HWS-POA.pdf](https://storage.googleapis.com/google-code-attachments/origami-pdf/issue-28/comment-0/HWS-POA.pdf)