Determine if a file is open

How can I easily determine if a file is already open before I try to open it programatically.

Specifically, my program involves displaying pdf files in Acrobat Reader.  If the user already has one the pdf file open, how can detect that?

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Try this:

function IsFileInUse(FileName: TFileName): Boolean;
  HFileRes: HFILE;
  Result := False;
  if not FileExists(FileName) then Exit;
  HFileRes := CreateFile(PChar(FileName),
                         GENERIC_READ or GENERIC_WRITE,
  Result := (HFileRes = INVALID_HANDLE_VALUE);
  if not Result then

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usual a try to open the file exclusive should tell you if you can do this,
if you can -> the file is not in use
if you not can -> the file is use

guess this does the suggestion of  Johnjces already,
it could be done with a TFileStream aslo

meikl ;-)
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