Name
  doc:SetEncryptionMode -- set document encryption mode
Synopsis

      status = doc:SetEncryptionMode(mode[, keylen])

Function
  `doc:SetEncryptionMode()` set the encryption mode. As a side effect, it ups the version of PDF to 1.4 when the mode is set to `#HPDF_ENCRYPT_R3`.

  The following encryption modes are currently supported:

  `#HPDF_ENCRYPT_R2:`
    Use "Revision 2" algorithm. `keylen` is automatically set to 5 (40 bits).

  `#HPDF_ENCRYPT_R3:`
    Use "Revision 3" algorithm. `keylen` can be 5 (40 bits) to 16 (128bits).

  When `doc:SetEncryptionMode()` succeeds, it returns `#HPDF_OK`. Otherwise, it returns an error code and the error handler is called.

Inputs
  mode
    one of the encryption modes listed above
  keylen
    specify the byte length of encryption key; only needed for `#HPDF_ENCRYPT_R3` (defaults to 5, i.e. 40 bits)
Results
  status
    status code
Errors
  `#HPDF_INVALID_DOCUMENT` - An invalid document handle was set.

  `#HPDF_INVALID_ENCRYPT_KEY_LEN` - An invalid key length was specified.

  `#HPDF_FAILED_TO_ALLOC_MEM` - Memory allocation failed.

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