It saves it in a temporary folder somewhere on the user's machine. Exactly where depends on the OS and version of Acrobat.
It is important to be aware of the conditions under which the cached FDF is created and removed. The FDF gets created if the document's "dirty" flag gets set to true and is true at the time that the user navigates away from the form and it is closed, assuming the user preference allows it and the nocache document property is not set to true (false or undefined). The dirty flag is automatically set to true whenever any field value changes or there is some other type of change, such as adding an annotation or altering the contents of a list/combo box. Also, note that the no cache user preference and the nocache property was new to Acrobat (Reader) 7.
When the user navigates away from a PDF that is viewed in a browser, Acrobat remained loaded for some time (~10 min), but was not visible unless the user otherwise had a PDF opened locally. After about ten minutes, Acrobat would auto shut-down and take any cached FDFs that may have been create with it, assuming it closed down normally and didn't crash before it deleted any cached FDFs.
Before Acrobat 7, the best you could do to control the creation of the cached FDF was to programmatically set the document's dirty flag to false in an attempt to get it to be false at the time the document closed. This meant sprinkling that line of code all over the place. This obviously was not a 100% reliable approach, but it did help. Also, auto-resetting the form when it was loaded helped too.
It is important to be aware of the conditions under which the cached FDF is created and removed. The FDF gets created if the document's "dirty" flag gets set to true and is true at the time that the user navigates away from the form and it is closed, assuming the user preference allows it and the nocache document property is not set to true (false or undefined). The dirty flag is automatically set to true whenever any field value changes or there is some other type of change, such as adding an annotation or altering the contents of a list/combo box. Also, note that the no cache user preference and the nocache property was new to Acrobat (Reader) 7.
When the user navigates away from a PDF that is viewed in a browser, Acrobat remained loaded for some time (~10 min), but was not visible unless the user otherwise had a PDF opened locally. After about ten minutes, Acrobat would auto shut-down and take any cached FDFs that may have been create with it, assuming it closed down normally and didn't crash before it deleted any cached FDFs.
Before Acrobat 7, the best you could do to control the creation of the cached FDF was to programmatically set the document's dirty flag to false in an attempt to get it to be false at the time the document closed. This meant sprinkling that line of code all over the place. This obviously was not a 100% reliable approach, but it did help. Also, auto-resetting the form when it was loaded helped too.