title: Data encoding when submitting a PDF form using AcroForm technology
body: <p>When I create a PDF form (for instance using Acrobat) that contains text fields in AcroForm format (PDF dictionaries, no XFA), and I submit the data to a server, how can I specify/retrieve the encoding that will be used?</p>
  
  <p>For instance. When I submit the Chinese glyphs '测试' (test), I receive the following headers and content on the server-side:</p>
  
  <pre><code>accept: application/x-ms-application, image/jpeg, application/xaml+xml, image/gif, image/pjpeg, application/x-ms-xbap, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*
  content-type: application/x-www-form-urlencoded
  content-length: 23
  acrobat-version: 10.1.4
  user-agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; MDDC; .NET4.0C; AskTbCLA/5.15.1.22229)
  accept-encoding: gzip, deflate
  connection: Keep-Alive
  Song=%b2%e2%ca%d4&amp;Test=
  </code></pre>
  
  <p>There's no reference to an encoding, except x-www-form-urlencoded. The two glyphs are represented as four bytes: B2 E2 CA D4. After some investigation, I know that B2E2 is the GBK value for the first glyph, and CAD4 the GBK value for the second glyph, but I can't derive this from the request header.</p>
  
  <p>Is it always GBK? I want to change the data encoding by setting a specific key in a dictionary in the PDF, but there doesn't seem to be any. For instance: I would like make sure the PDF always sends Unicode characters instead of GBK.</p>
  
  <p>Note that I've already experimented by changing the default font (and encoding) of the text field. I've also searched ISO-32000-1 for encodings in fields, but all I found was a way to define non-Latin characters for check boxes, and some info about the encoding of an FDF file. None of which answered my questions.</p>