I have obtained Prime 3 and converted a few files. The functionality appears to be nearly equal to Mathcad 15. The main deficiencies at this time are with plots and style sheets. The capability to make plots is present, but some of the flexibility with legends and titles is gone. Styles for headings, titles, etc. are also missing. Hopefully, the missing features will appear in a later version.
In the previous post, I included the appendices from my book in Mathcad 15 format. The new Prime 3 versions are included below. For instructions in downloading the .mcdx files, use the procedure shown here. In the last step, change the extension to .mcdx.