You are sure that the text files in a folder contain a certain string, but the Windows Explorer search doesn’t return anything! WTF?
Maybe, the files just have an extension which Windows doesn’t recognize, and are therefore skipped. This is a hack to enable Windows Explorer to search in all files, not just with extensions that are registered:
reg add HKLMSYSTEMCurrentControlSetControlContentIndex /v FilterFilesWithUnknownExtensions /t REG_DWORD /d 1
And this is the code to disable the behaviour:
reg add HKLMSYSTEMCurrentControlSetControlContentIndex /v FilterFilesWithUnknownExtensions /t REG_DWORD /d 0