If Foxit PDF IFilter stops working with successful installation, there may be two reasons.
I. Windows Update has changed Foxit PDF IFilter GUID to a default GUID that is not supported by Foxit PDF IFilter.
Solution (for SharePoint):
Change GUID back to the Foxit PDF IFilter’s value which is {987f8d1a-26e6-4554-b007-6b20e2680632}. You can follow the steps as below:
A. Locate the following registry subkeys and then check the (Default) value.
(For SharePoint 2010)
HKEY_LOCAL_MACHINESOFTWAREMicrosoftSharedToolsWebServerExtensions14.0
Search SetupContentIndexCommonFiltersExtension.pdfHKEY_LOCAL_MACHINESOFTWAREMicrosoftOfficeServer14.0
SearchSetupContentIndexCommonFiltersExtension.pdf
HKEY_LOCAL_MACHINESOFTWAREMicrosoftSharedToolsWebServerExtensions14.0
SearchSetupFilters.pdf
(For SharePoint 2007)
HKEY_LOCAL_MACHINESOFTWAREMicrosoftSharedToolsWebServerExtensions12.0
SearchSetupContentIndexCommonFiltersExtension.pdf
HKEY_LOCAL_MACHINESOFTWAREMicrosoftShared ToolsWeb Server Extensions12.0
SearchSetupFilters.pdf
B. Change the (Default) value to {987f8d1a-26e6-4554-b007-6b20e2680632}
C. To make the changes take effect, do an IISreset, stop and restart search service.
D. Perform crawling and then a search.
II. Foxit PDF IFilter has not been licensed successfully.
Foxit PDF IFilter will stop working if the license becomes invalid. It may because the trial expires and you have not activated your IFilter with a code/license key. Please check whether your IFilter has been licensed.