>i dont think so sergey the text says : enter the signature in hexadecimal format with a max of 8 bytes for ex 1A 00 00 03 00 00 14 00. the signature offset should be zzero relative and less than 512 bytes

I think the software you're using is looking for some sort of header, like the "MZ" that DOS/Windows executables have, or the "PK" in the zips, or "...JFIF" in the jpg files.

No such luck - dbf/cdx/fpt have a specific header in their own manner, with the first dozen bytes taken for various integers describing the lengths and offsets of various blocks within the files, so they can be anything.