Want to create hatch *.pat file, open an preexisting file, a functional pattern file, whit notepad, no modification done & saved as *.pat extension (other name to avoid damage to original) and AutoCAD says (for the new one) "error in pattern file". Any idea to solve it? (None of the 4 encoding options from notepad work)(Currently using AutoCAD Architecture 2017)

Is it a one-pattern .pat file?  If so, the name of the file [+ the .pat] must be exactly the same as the pattern name.  So if you change the name of the file, change the name of the pattern defined in it, to match.