You can PDF files to any folder you'd like. There are several "Default" folder for special purposes. The Default directory where a file will be stored on a SaveAs, floats. I think it's something like, the current folder for the file, whatever was last used, or MyDocuments, depending on what's available.
This is also another suggestion to change the default directory where docs are stored in the following post title [url=http://www.acrobatusers.com/forums/aucbb/viewtopic.php?id=3738]default file location[/url]
Or, if you are able to modify the system registry (not supported by Adobe) you can use the following tip from Developer Support for [url=http://support.adobe.com/devsup/devsup.nsf/docs/51608.htm]Setting default directory for opening files[/url].
Lori Kassuba is an AUC Expert and Community Manager for AcrobatUsers.com.
Thom Parker
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