>I need to check for the presence of the PDFWriter as my app is used on other machines

You would need to look for ACROBAT.EXE. Those who only have the reader will not have that file as the reader is named something like AcroRd32.exe. You can use the registry class to see what the value is of HKEY_CLASSES_ROOT\Applications\Acrobat.exe\shell\open. Since I do have it installed, mine returns a value of "C:\Program Files\Adobe\Acrobat 4.0\Acrobat\Acrobat.exe" "%1".