Check pdf validity using ghostscript

check-pdf-validity.sh

gs -dNOPAUSE -dBATCH -sDEVICE=nullpage valid.pdf
GPL Ghostscript 9.16 (2015-03-30)
Copyright (C) 2015 Artifex Software, Inc.  All rights reserved.
This software comes with NO WARRANTY: see the file PUBLIC for details.
Processing pages 1 through 1.
Page 1

(return code 0)

: gs -dNOPAUSE -dBATCH -sDEVICE=nullpage invalid.pdf
GPL Ghostscript 9.16 (2015-03-30)
Copyright (C) 2015 Artifex Software, Inc.  All rights reserved.
This software comes with NO WARRANTY: see the file PUBLIC for details.
   **** This file uses an unknown security handler.
   **** The file was produced by:
��+dr��� <<<<��.]��{[1$3�*M=��]H&T��v�U@�r�,t�
Error: /undefined in pdf_process_Encrypt
Operand stack:

Execution stack:
   %interp_exit   .runexec2   --nostringval--   --nostringval--   --nostringval--   2   %stopped_push   --nostringval--   --nostringval--   --nostringval--   false   1   %stopped_push   1951   1   3   %oparray_pop   1950   1   3   %oparray_pop   1934   1   3   %oparray_pop   --nostringval--   --nostringval--   --nostringval--   --nostringval--   false   1   %stopped_push   --nostringval--
Dictionary stack:
   --dict:1182/1684(ro)(G)--   --dict:1/20(G)--   --dict:83/200(L)--   --dict:83/200(L)--   --dict:117/127(ro)(G)--   --dict:280/300(ro)(G)--   --dict:22/32(L)--
Current allocation mode is local
Last OS error: Invalid argument
GPL Ghostscript 9.16: Unrecoverable error, exit code 1
:

(return code 1)

I know you were here for this.... 👀

exec("gs -dNOPAUSE -dBATCH -sDEVICE=nullpage {$pdf_filename}", $output, $return_var);
  if($return_var) {
    // error handling
  }