title: How to understand pdf forms flags?
body: <p>I read pdf structure using <code>pdfbox</code> and I can't find out some data from stream:</p>
  
  <pre><code>1 g
  0 0 18 18 re
  f
  0.5 0.5 17 17 re
  s
  q
  1 1 16 16 re
  W
  n
  0 g
  BT
  /ZaDb 14.532 Tf
  2.853 4.081 Td
  13.9943 TL
  (4) Tj
  ET
  Q
  </code></pre>
  
  <p>It is stream information about checkbox but what does it mean that letters?
  Can anyone explain to me or it would be better if you can share with me where I can read about it?
  <a href="https://i.stack.imgur.com/Qpp8u.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Qpp8u.png" alt="enter image description here"></a></p>