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:diretorioFILE.EXT','C:diretorioFILE.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;