Arbitrary Editor for Mac I need a text editor on mac that could open arbitrary file and show its content. 

Edit: I dont want to "decode" the files, I just want to read them byte by byte, as they are sitting on the filesystem, just like fopen() in c. (No parsing!) Is there any editor that can do that?

For example, I want to open "test.pages" file, because I am curious. Textedit denied to open it, textWrangler opened it in disk browser. TextMate did open it , showing first 2 characters as PK, (which i understand as a packed file), but it showed lots of special characters as white spaces, which is not acceptable.

Notepad (or any XYZ editor on windows) could open arbitrary files, without ever complaining about "format".
This seems to be the job for a hex viewer/editor rather than a text editor. An easy way to do this would be just to use Terminal emacs with hex mode.

If you prefer a GUI application Hex Fiend looks promising


  
  A fast and clever open source hex editor for Mac OS X.
  Insert, delete, rearrange.  Hex Fiend does not limit you to in-place changes like some hex editors.
  Work with huge files.  Hex Fiend can handle as big a file as you’re able to create.  It’s been tested on files as large as 118 GB.
  Small footprint.  Hex Fiend does not keep your files in memory.  You won’t dread launching or working with Hex Fiend even on low-RAM machines.
  Binary diff.  Hex Fiend can show the differences between files, taking into account insertions or deletions.
  Data inspector.  Interpret data as integer or floating point, signed or unsigned, big or little endian...