Adobe have a tendency to change or break in each successive Acrobat release the means by which third parties can automate PDF printing. PDF conversion is currently done by the following methods:

Acrobat Prof X, XIuses object linking and embedding (OLE)
Adobe Reader X, XI, DCspawns ACRORD32.EXE
Acrobat Prof. v8, v9uses object linking and embedding (OLE)
Adobe Reader v8, v9uses dynamic data exchange (DDE)
Acrobat Prof. v6, v7:uses object linking and embedding (OLE)
Adobe Reader v6, v7: spawns ACRORD32.EXE
Acrobat v5 uses object linking and embedding (OLE)
Acrobat Reader v5 uses dynamic data exchange (DDE)
Acrobat v4 spawns ACROBAT.EXE
Acrobat Reader v4 spawns ACRORD32.EXE
Acrobat v3 & earlier not currently supported

Note that the COPIAFACTS.INI entries used to specify path overrides for earlier releases are no longer used. If you have both Acrobat and the reader installed, Adobe will now normally use Acrobat even if you try to specify that Adobe Reader is to be used. We do not support installations where these two applications have different Adobe version numbers, although some may work.

If you install an Adobe product specially for the purpose of document conversion, be sure to run it first to view some PDF documents so that you get past the pop-up dialog which invites you to register. Some versions of Acrobat do a regular version-update check which requires user confirmation. You should ensure that this is disabled if you use Acrobat or Adobe Reader for PDF conversions.

Adobe Reader X and later users should UNCHECK 'Enable Protected Mode at startup' in Edit / Preferences.  This setting may be in 'General' or 'Security (enhanced)'.
Adobe Reader DC users should visit the Edit / Preferences and visit every category page to ensure that any setting capable of showing pop-ups and warnings is disabled, and that all settings to suppress warnings and messages are enabled..

For early versions of Adobe software we recommend moving many of the Acrobat plug-ins out of the PLUG_INS folder to significantly speed up operations on the machine running FFEXTERN, although this may of course reduce functionality if you need to use the program interactively on the same machine. In Reader V6 the plug-ins may be moved to the Optional folder from where they will be loaded on demand.

If you have Acrobat Professional v6 or later installed, you can use it for rendering non-faxable TIF files by specifying convert option TIFAcrobat.

Files to be converted by Acrobat or Adobe Reader must contain a valid PDF signature in the file header. To override this check to convert unusual files formats supported by Acrobat, add an FS variable CVT_NOSIGCHECK to the FS file controlling the conversion.  With this value specified, specifying as PDF a format unknown to Acrobat can result in huge numbers of output pages - use at your own risk!  The internal converter does not use this check.