C#

int length;
byte[] bt=new byte[1024];
FileStream input=new FileStream("in.pdf", FileMode.Open);
FileStream output=new FileStream("out.pdf", FileMode.Create);

BinaryReader rd= new BinaryReader(input);
BinaryWriter rw=new BinaryWriter(output);

rd.Read(bt, 0, 55);

while(true)
{
  length=rd.Read(bt, 0, 1024);
  if (length==0) break;
  rw.Write(bt);
}
rd.Close();
rw.Close();

input.Close();
output.Close();

byte[] x= File.ReadAllBytes("C:\\test.pdf"); //opens the file
byte[] temp = new byte[x.Length - 55]; //creates new byte array with the new size (minus 55 bytes)
long tempx = 0; // couter for the new array position
for (long i = 55; i < x.LongLength; i++) // for loop which starts after 55 byte. 
{
   temp[tempx] = x[i]; // rewritting the new file with byte from 56 and on..
   tempx++; // the counter for the new byte array
}
File.WriteAllBytes("C:\\test.pdf", temp); //after the loop, the new file is written

************* Exception Text **************<br />
System.IO.IOException: The process cannot access the file 'C:\Documents and Settings\milos\My Documents\Visual Studio 2008\Projects\Brisanje Bytov iz datotek\Brisanje Bytov iz datotek\bin\Debug\New Folder\export_104974_00001484.pdf.e3.blob.pdf' because it is being used by another process.<br />
   at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)<br />
   at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy)<br />
   at System.IO.FileStream..ctor(String path, FileMode mode)<br />
   at Brisanje_Bytov_iz_datotek.Form1.button2_Click(Object sender, EventArgs e) in C:\Documents and Settings\milos\My Documents\Visual Studio 2008\Projects\Brisanje Bytov iz datotek\Brisanje Bytov iz datotek\Form1.cs:line 37<br />
   at System.Windows.Forms.Control.OnClick(EventArgs e)<br />
   at System.Windows.Forms.Button.OnClick(EventArgs e)<br />
   at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)<br />
   at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)<br />
   at System.Windows.Forms.Control.WndProc(Message& m)<br />
   at System.Windows.Forms.ButtonBase.WndProc(Message& m)<br />
   at System.Windows.Forms.Button.WndProc(Message& m)<br />
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)<br />
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)<br />
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)<br />

for (int c = 0; c < listBox1.Items.Count; c++)
           {
               listBox1.SelectedItem = c;
               int length;
               byte[] bt = new byte[1024];
               FileStream input = new FileStream(listBox1.Text, FileMode.Open);

               FileStream output = new FileStream(listBox1.Text + ".new", FileMode.Create);

               BinaryReader rd = new BinaryReader(input);
               BinaryWriter rw = new BinaryWriter(output);

               rd.Read(bt, 0, 55);

               while (true)
               {
                   length = rd.Read(bt, 0, 1024);
                   if (length == 0) break;
                   rw.Write(bt);
               }
               rd.Close();
               rw.Close();

               input.Close();
               output.Close();
           }

btn_Start_Click(object sender, EventArgs e)
{
   Thread th = new Thread(new ThraedStart(Download));
   th.Start();

   if (th.ThreadState == ThreadState.Running) // Here i am Disabling
   btn_Start.Enabled = false;
}

public void Download()
{
   // Here i wrote logic for downloading files.
   this.Invoke((MethodInvoker)delegate
   {
       btn_Start.Enabled = true;
   });

}