请教一下base64解码后生成pdf文件的问题

[songjg]

为什么这样写生成的文件提示格式错误，里面解码出来的都是乱码？请高手给个思路！
procedure TForm1.Button5Click(Sender: TObject);
var
m1:TMemoryStream;
m2:TFileStream;
SS:TStringStream;
begin
m1:=TMemoryStream.Create;
SS:=TStringStream.Create(Memo1.Lines.Text);
DecodeStream(ss,m1);
m2:= TFileStream.Create('E:\pdf.pdf', fmCreate);
m2.Position:=0;
m2.Write(m1,m1.Size) ;
m1.Free;
m2.Free;