It is likely that the most common sme to txt conversion is related to export of messages or contacts from a .sme backup (Samsung Kies) to a text file (usually in some structured format, such as CSV). As far as we know, this should be possible using Kies, or at least in some of the older versions of the program.
Additionally, programs like the SmartEncryptor use .sme files as well, but it is unlikely that these encrypted archives could be converted to some text format (.txt) directly. However, it might be possible that some text files are located inside the encrypted .sme file. If that is the case, you will need to decrypt and extract the archive using SmartEncryptor, no converter will help you.Open SME file Open TXT file