I open a PHP file in ANSI format and change the encoding to UTF-8 no BOM, then
save it. 
When I reopen it, it is still in the old format. 
I also tried the batch conversion, but the result is the same. 

are there some specific characters other than ASCII -  basic Latin, numbers
There normally a detection for encoding, which should recognise utf-8, but for
those "lower" characters without accents etc. the file is the same even in
different encodings.
Do you get get some corrupted text due to the bad encoding onreopening the file
or is it just the displayed encoding in the satutsbar?
I believe, PSPad can keep the previously selected encoding for a given file,
according to the settings:
Settings: Files and Dirs: [x ] Remember File state


PSPad freeware editor

Odpovedet emailem