RIS file are special ASCII text files that contain citation references. You can use text from any source (TXT, PDF, DOC etc.) and simply copy and paste (or import if possible) relevant text data to a program that can generate RIS citations, for example the Reference Manager from Thomson Reuters.
Unfortunately, we do not know about any programs capable of direct txt to ris conversion.Open TXT file Open RIS file
Bibliographic reference and citation management software