Mat Hoffman .pkr files-
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4 byte = PKR3 = 0x33524b50
4 byte = offset to the Directory Listing Header
Then starts file data

Directory Listing Header:
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12 bytes total
4 bytes - unknown 04000000 --> 0x00000004
4 bytes - total number of directories
4 bytes - total number of files

Directory Listing Structure:
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40 bytes total each directory list entry.
32 bytes - string: directory name
4 bytes - count of the total files (suma de los archivos hasta el momento)
4 bytes - number of files in the directory

File Listing Structure:
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52 bytes total each file list entry
32 bytes - string: file name
4 bytes - CRC32
4 bytes - 0xfffffffe Uncompressed  0x00000002 Compressed (Zip Normal Wrar)
4 bytes - offset to the file data
4 bytes - uncompressed file size
4 bytes - compressed file size

data.pkr 
33 dirs
1510 files

media.pkr
3 dirs
20 files