I normally do something like this:

[pascal]const
TFileVersion : array [0..19] of char = ( .... )
...

procedure LoadFile()
BlockRead( F, FileVersion, SizeOf(TFileVersion), dataRead );
if FileVersion <> TFileVersion then
begin
end;[/pascal]

TFileVersion is always the first thing I write to the file, it also has the nice advantage that when you look at the file with a simple text editor you’ll be able to read that text.