PAK

The PAK (Package) File format is Pangya: Fantasy Golfs archive/packaging format. The PSP archive consists of two files psppackfilelist.pak and pspdata.pak

psppackfilelist.pak

As the name suggests, it contains the list of files of the archive. Inside the file, you read following structure until the end of the file:

public struct FileEntry
{
    public ushort Type;
    public ushort Unknown1;
    public uint Offset;
    public uint FileSize;
    public uint RealFileSize;
    public string FileName;
}

pspdata.pak

Use the acquired FileEntries from psppackfilelist.pak to read the data. Just start reading FileSize from Offset and save it to FileName. There is no compression or encryption, that's why FileSize and RealFileSize match for all entries.