In Windows, I often use copying a piece of text into notepad as a way of removing special charachters that can cause trouble. This became a much more urgent problem in Android six months or so ago, when Android started rejecting any effort to rename a file that contained one or more forbidden printing or non-printing characters such as a colon or a carriage return. This change was not accompanied by any change to indicate what or where the problem character is. Since I often try to rename PDF files with the real name of the document, copied from within the document, this has been a huge inconvenience. Is there any android text editing spp that removes or renders visible illegal characters as notepad does? Or has anyone found a good solution to this problem?