TODO

Comparison with pdftk features:
[x] = done, [?] = maybe, [ ] = to do

[ ] Python 3 Support (pypdf can do it, I think)
[x] Merge PDF Documents
[x] Split PDF Pages into a New Document
[x] Rotate PDF Pages or Documents
[x] Decrypt Input as Necessary (Password Required)
[x] Encrypt Output as Desired
[?] Fill PDF Forms with FDF Data or XFDF Data and/or Flatten Forms
[?] Apply a Background Watermark or a Foreground Stamp
[ ] Report on PDF Metrics such as Metadata, Bookmarks, and Page Labels
[?] Update PDF Metadata
[?] Attach Files to PDF Pages or the PDF Document
[?] Unpack PDF Attachments
[x] Burst a PDF Document into Single Pages
[ ] Uncompress and Re-Compress Page Streams
[x] Repair Corrupted PDF (Where Possible)

Known issues:
- The same page of the same input file cannot be added to the output twice
  with two different rotations (e.g., ``cat foo.pdf 1R 1D`` won't do what
  you'd hope).