C# 从文件路径中获取文件类型名称

我已经实现了从文件路径中获取文件类型名称所需的所有代码，它运行成功，但它返回减去的类型名称，例如，如果.pdb 或 .pdf文件的文件路径，那么它将返回“obe Acrobat Document”而不是“Adobe Acrobat文档”

我用过shell32.dll。我不明白发生了什么，请帮我摆脱它。

源代码：

[StructLayout(LayoutKind.Sequential, CharSet=CharSet.Auto)]
    internal struct SHFILEINFO
    {            
        public IntPtr hIcon;            
        public IntPtr iIcon;            
        public uint dwAttributes;            
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)]
        public string szDisplayName;            
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 80)]
        public string szTypeName;
    };

internal class Win32
{            
    public const uint FILE_ATTRIBUTE_NORMAL = 0x80;            
    public const uint FILE_ATTRIBUTE_DIRECTORY = 0x10;            
    public const uint SHGFI_TYPENAME = 0x000000400;            
    public const uint SHGFI_USEFILEATTRIBUTES = 0x000000010;            
    internal const uint SHGFI_SYSICONINDEX = 0x000004000;            
    internal const int ILD_TRANSPARENT = 0x1;            
    internal const uint SHGFI_ICON = 0x100;            
    internal const uint SHGFI_LARGEICON = 0x0; 
    internal const uint SHGFI_SMALLICON = 0x1; 

    [DllImport("shell32.dll", CharSet=CharSet.Unicode)]
    internal static extern IntPtr SHGetFileInfo
        (
            string pszPath, 
            uint dwFileAttributes, 
            ref SHFILEINFO psfi, 
            uint cbSizeFileInfo, 
            uint uFlags
        );

    [DllImport("shell32.dll", CharSet = CharSet.Auto)]
    internal static extern int ExtractIconEx
        (
            string stExeFileName, 
            int nIconIndex, 
            ref IntPtr phiconLarge, 
            ref IntPtr phiconSmall, 
            int nIcons
        );

    [DllImport("comctl32.dll", SetLastError = true)]
    internal static extern IntPtr ImageList_GetIcon
        (
            IntPtr himl, 
            int i, 
            int flags
        );

    [DllImport("user32.dll")]
    internal static extern bool DestroyIcon(IntPtr hIcon);
}

internal static string GetFileType(string filename)
{
    SHFILEINFO shinfo = new SHFILEINFO();
    Win32.SHGetFileInfo
        (
                filename,
                Win32.FILE_ATTRIBUTE_NORMAL,
                ref shinfo, (uint)Marshal.SizeOf(shinfo),
                Win32.SHGFI_TYPENAME |
                Win32.SHGFI_USEFILEATTRIBUTES
            );

    return shinfo.szTypeName; //It return "obe Acrobat Document" Instead of "Adobe Acrobat Document"
}