@Claudia-Svenson said:
I would have expected from such a feature-rich tool like NP++ That I can mark/select just a part of the full text and convert it in-place to a new encoding (by a new menu or via smart via described earlier). All that without switching back and forth encoding and using clipboard.
Probably there is no such tool included because this is a situation that should very, very rarely happen. One file normally contains one encoding — that applies everywhere, not just in Notepad++. (I believe there are some legacy exceptions for East Asian languages, but in those cases the encodings themselves include bytes that describe the encoding changes. To the best of my knowledge, Scintilla, and therefore Notepad++, does not support them.)
If this is happening to you often enough to be a concern, I urge you to look earlier in your process. How are you winding up with files which contain characters in more than one encoding?
As you can see from this demonstration, copying text from one encoding and pasting it into a document with a different encoding ordinarily converts the text to the encoding into which you paste it. So just copying and pasting from some other source should not cause this problem.
I am not ruling out that there could be a bug, whether in Notepad++ or in some other program, that is causing you to get wrongly-encoded text in a file. If so, we should identify that bug. (Especially if it turns out to be in Notepad++, where possibly it could be fixed.)
It is also possible that there is a step in whatever procedures you are following that predictably causes this, like concatenating two files with some other tool without first making sure the files have the same encoding, or using Edit | Paste Special | Copy/Cut/Paste Binary Content inappropriately.
If someone else is supplying you with files that contain multiple encodings and you can’t prevail upon them to correct their procedures, then using a Python script, as @mpheath suggested, is probably the best solution.