[DllImport("kernel32.dll")]
static extern uint GetFileSize(IntPtr hFile, IntPtr lpFileSizeHigh);
[DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)]
public static extern IntPtr CreateFileMapping(
    IntPtr hFile,
    IntPtr lpFileMappingAttributes,
    FileMapProtection flProtect,
    uint dwMaximumSizeHigh,
    uint dwMaximumSizeLow,
    [MarshalAs(UnmanagedType.LPTStr)]string lpName);
[Flags]
public enum FileMapProtection : uint
{
    PageReadonly = 0x02,
    PageReadWrite = 0x04,
    PageWriteCopy = 0x08,
    PageExecuteRead = 0x20,
    PageExecuteReadWrite = 0x40,
    SectionCommit = 0x8000000,
    SectionImage = 0x1000000,
    SectionNoCache = 0x10000000,
    SectionReserve = 0x4000000,
}
[DllImport("kernel32.dll", SetLastError = true)]
static extern IntPtr MapViewOfFile(
    IntPtr hFileMappingObject,
    FileMapAccess dwDesiredAccess,
    uint dwFileOffsetHigh,
    uint dwFileOffsetLow,
    uint dwNumberOfBytesToMap);
[Flags]
public enum FileMapAccess : uint
{
    FileMapCopy = 0x0001,
    FileMapWrite = 0x0002,
    FileMapRead = 0x0004,
    FileMapAllAccess = 0x001f,
    fileMapExecute = 0x0020,
}
[DllImport("psapi.dll", SetLastError = true)]
public static extern uint GetMappedFileName(IntPtr m_hProcess, IntPtr lpv, StringBuilder 
        lpFilename, uint nSize);
[DllImport("kernel32.dll", SetLastError = true)]
static extern bool UnmapViewOfFile(IntPtr lpBaseAddress);
[DllImport("kernel32.dll", SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool CloseHandle(IntPtr hObject);
public static string GetFileNameFromHandle(IntPtr FileHandle)
{
    string fileName = String.Empty;
    IntPtr fileMap = IntPtr.Zero, fileSizeHi = IntPtr.Zero;
    UInt32 fileSizeLo = 0;
    fileSizeLo = GetFileSize(FileHandle, fileSizeHi);
    if (fileSizeLo == 0)
    {
        // cannot map an 0 byte file
        return "Empty file.";
    }
    fileMap = CreateFileMapping(FileHandle, IntPtr.Zero, FileMapProtection.PageReadonly, 0, 1, null);
    if (fileMap != IntPtr.Zero)
    {
        IntPtr pMem = MapViewOfFile(fileMap, FileMapAccess.FileMapRead, 0, 0, 1);
        if (pMem != IntPtr.Zero)
        {
            StringBuilder fn = new StringBuilder(250);
            GetMappedFileName(System.Diagnostics.Process.GetCurrentProcess().Handle, pMem, fn, 250);
            if (fn.Length > 0)
            {
                UnmapViewOfFile(pMem);
                CloseHandle(FileHandle);
                return fn.ToString();
            }
            else
            {
                UnmapViewOfFile(pMem);
                CloseHandle(FileHandle);
                return "Empty filename.";
            }
        }
    }
    return "Empty filemap handle.";
}