Copiando Arquivos Via Programação

Function CopiaArquivo(scrname,destname:string):byte;
var
  source,destination:file;
  buffer:array[1..1024] of byte;
  readcnt,writecnt:word;
  pname,dname,fname,ename:String;
  { USO: R:=COPIAARQUIVO('C:\diretorio\FILE.EXT','C:\diretorio\FILE.EXT'); Devolve 0=Ok, 1=Erro no Origem, 2=Erro no Destino, 3=Disco Cheio }
begin
  AssignFile(source,scrname);
  Try
  Reset(source,1);
  Except
  CopiaArquivo:=1;
  Exit;end;If destname[length(destname)]='\' then
  begin
  pname:=scrname;
  destname:=destname+separa(scrname,'\',Ocorre(scrname,'\')+1);
  end;
  AssignFile(destination,destname);
  Try
  Rewrite(destination,1);
  Except
  CopiaArquivo:=2;
  Exit;
end;
Repeat
  BlockRead(source,buffer,sizeof(buffer),readcnt);
  Try
  BlockWrite(destination,buffer,readcnt,writecnt);
  Except
  CopiaArquivo:=3; {Disco Cheio?}
  Exit;
end;
until (readcnt=0) or (writecnt<>readcnt);
CloseFile(destination);
CloseFile(source);
CopiaArquivo:=0;
end;