I don't think that will work.
An (older) Mathcad .MCD file is either an ASCII file (up to and including Mathcad 6) or a binary file (until at least Mathcad 11) the structure definition of which was never published. The (newer) Mathcad .XMCD file is an XML structured file. I should expect that Mathcad 14 and 15 will complain about the file contents, when the contents of a .MCD file is presented to them as a .XMCD file.
And, while I value Notepad++, I don't think it is capable of translating any of the .MCD structures to XML. I would be very happy if it did...
I guess that nileshwankhade after more than 11 years already succeeded in converting the files - which way ever. Furthermore the suggested procedure using Notepad++ (I also doubt that it will do any conversion) is exactly what nileshwankhade tried to avoid - was asking for command line solution to be able to automate the procedure.
Not sure what @Sonther actually tried, but you are absolutely correct that opening a *.mcd file just renamed to *.xmcd results in an error when trying to open it with Mathcad 14 or 15 ("is not a valid XML Document").
Might be you are right he was trying to automate the process as he actually pointed out not wanting to use "Save As".
Reason I converted using Notepad++ was because I were having trouble opening the files in Mathcad. And couldn't use Mathcad to Save As. But Notepad++ did manage to convert the files using Save As and I could read the files in Mathcad afterwards.
All in all, it worked for me 😄
Can someone please help me to convert this file, so that I can Open it in PTC Mathcad Prime 5.0.0...i cannot open the mcd files or convert them.