1. Load Cryptor DLL, but don´t register the list of files yet. 2. Try to USE the DBF file: If no error Close the file and proceed with encryption DBF and FPT else Assume a file is already encrypted You also should detect "Not a Table" and "Invalid memo file" errors, in order to know which file is or is not encrypted DBF or FPT Close Files and Encrypt the file which didn´t generate errors. endif 3. Register the list in Cryptor DLLThis way, you can run the encryption routine n-times and encrypt only once.