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I usually define functions that correspond to the types/blocks in the defined file format and use those to read it piece by piece. For this, I created some readDWORD, readWORD, and readGUID functions. The GUID took a bit to figure out, and I'm still not 100% sure it's correct but it makes some sense and matches your example. <?php $file = 'test.utx'; $fp = fopen($file, 'rb'); $sig = readDWORD($fp); if ($sig !== 0x9E2A83C1){ die('Invalid file format'); } else { echo 'Valid file.' . PHP_EOL; } echo 'Version: ' . ($version = readWORD($fp)) . PHP_EOL; echo 'License mode: ' . readWORD($fp) . PHP_EOL; echo 'Package flags: ' . readDWORD($fp) . PHP_EOL; echo 'Name count: ' . readDWORD($fp) . PHP_EOL; echo 'Name offset: ' . readDWORD($fp) . PHP_EOL; echo 'Export count: ' . readDWORD($fp) . PHP_EOL; echo 'Export offset: ' . readDWORD($fp) . PHP_EOL; echo 'Import count: ' . readDWORD($fp) . PHP_EOL; echo 'Import offset: ' . readDWORD($fp) . PHP_EOL; if ($version >= 68){ echo 'GUID: ' . readGUID($fp) . PHP_EOL; } function readDWORD($fp) : int{ return read($fp, 4, 'V'); } function readWORD($fp) : int{ return read($fp, 2, 'v'); } function readGUID($fp) : string{ $time_low=readDWORD($fp); $time_mid=readWORD($fp); $time_high_and_version=readWORD($fp); $clk_seq_hi_res=read($fp, 1, 'C'); $clk_seq_low=read($fp, 1, 'C'); $node=fread($fp, 6); return sprintf('%s-%s-%s-%s%s-%s' , bin2hex(pack('N', $time_low)) , bin2hex(pack('n', $time_mid)) , bin2hex(pack('n', $time_high_and_version)) , bin2hex(pack('C', $clk_seq_hi_res)) , bin2hex(pack('C', $clk_seq_low)) , bin2hex($node) ); } function read($fp, int $length, string $code){ $bytes = fread($fp, $length); $parsed = unpack($code . 'parsed', $bytes); return $parsed['parsed']; } The file specification you linked says the file is encoded in Little Endian. The UUID RFC says the representation is in Big Endian so we read the multi-byte components as little endian then convert them to big endian for display. output Valid file. Version: 127 License mode: 29 Package flags: 33 Name count: 31 Name offset: 72 Export count: 7 Export offset: 753 Import count: 6 Import offset: 711 GUID: e484d857-00b7-4107-a58a-36ff29f6a3a5