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Home / Is the Sumatra IFilter better than Windows 10 default?



Just wondering what the pros and cons of the Sumatra IFilter are - for indexing file contents to make them searchable. What exactly does it do differently, is there any way to find out?

I’ve been able to search pdfs adequately on Windows 10 - although never as perfectly as ctrl+F from within Chrome say (i.e some words that the document contains and can be found when viewed in Chrome are not included in Windows search)

Will Sumatra fix this? Is it easy to switch back to the default IFilter? What’s the most comprehensive of the different options?

Thanks so much - I’m doing open book exams at the moment so really want my documents to be searchable!


IFilters enhance the indexing system by allowing it to “see” the encoded internal contents of the files it recognizes in addition to those with “plain” text, so if index searching includes PDF “contents” the results will be significantly greater.

There is a good description and a comprehensive free for personal use Enterprise grade IFilter at

The “con” is that searching takes much longer to work through all the supported files contents.

The trick then is to only allow contents index search in restricted areas. More troublesome when your pdfs are dotted all over the system/users folders.

Personally I don’t usually do a system wide search for words, and would hazard a guess (although I have not tested) that any problems with searching within a file are multiplied by the system when searching through ALL indexed files.

Obviously each users experience will differ greatly based on system hardware / optimization / type of file structure. Thus impossible to say how much benefit they will get.
There should be no harm trying it then uninstalling to remove it if you decide it is not helping your usage of the normal search or too slow.

Just remember that independent of enabling in SumatraPDF that wherever you change the folder options to expand searching you could need to go back and UNdo those changes.


could please someone help me? I’ve been trying for days to make indexing work.
I have xchange-pdf editor and SumatraPDF installed. I have the filter appearing in the indexing option for file properties and content.
Then I tried adding specific folders like my User>Onedrive, Downloads, Documents and Desktop and rebuilt the index.

Currently nothing works but the filenames so unless there is the keyword in filename nothing shows up even when I select it on file explorer as an option to search contents. I just want to search for keywords in pdfs of a folder on my desktop.

Thank you


Key factor for any iFilters to work they should match the intended use thus 32bit for 32bit system or search app and 64bit for 64bit system they are registered and unregistered during installation and uninstallation. By default they are not installed by SumatraPDF, however, if that option is selected it is easy to have more than one wrong one. Although it is possible to need and install both, It is not a good idea to have more than one registered ifilter at a time so decide on one and remove/disable the others.

To enable/disable manually you can use Regsvr32 commands but most standard users are advised to use the relevant installer/uninstall options since they should include additional checks on privilege etc.

As you have indicated Windows needs to know which folders they are to be applied to so check the last option image each option can take extra time so here I am NOT searching in archives but have included “and contents” which can seriously slow down SumatraPDF IF I do a search when using file open. It is better to search using Windows Explorer then pass the found file to SumatraPDF to open from the known location.


So we should keep this option off if we want to be able to search inside files?



It depends on if you are using other filters (better ones)

Windows Desktop Search did not have the ability to decrypt the text inside searchable PDF, the feature needed to be added by Acrobat / SumatraPDF or another decryptor, so Windows Search can Search inside PDF.

I do not know if Win10 Edge adds that to Win 10 but IExplorer did not.

If you have a simple PDF with searchable text in a folder you can test windows search to see if it works. IF NOT finding known text content then try with that option added during installation.

Do not expect it will allow search to see ALL text, there are many reasons it will not work. Like if you copy and paste text from SumatraPDF is it garbled for many reasons, such as bad fonts or bad letter s p a c i n g. What you see in PDF is not WYSIWYG and may be rights restricted.