Limitations

HoudahSpot is based on Apple's Spotlight technology. It finds only what Spotlight can find. Apple chose to exclude some select system directories from the Spotlight index. By setting your privacy preferences you may have excluded some more.

Spotlight relies on importer plug-ins to index file content and metadata. Such importers are provided either by Apple or by the respective application authors. If you can't find a file by contents, you may lack the appropriate importer. Try searching for the file by name.