The doc tells me to copy and edit a source code file, but the code I see in my ProTop installation is encrypted or in procedure libraries; where's the source?
The standard ProTop installation includes encrypted source and procedure libraries for those without a development license who cannot compile (encrypted) source code on the fly. These folks will have to use _progres -rx to compile the code before it can be used.
Your ProTop installation includes the client-viewable and editable source code in a file named *src.zip.
To see the code, simply unzip the *src.zip into $PROTOP/src and then copy the code you are interested in according to the instructions.
For instance, to collect and report Custom Application KPIs, copy $PROTOP/src/lib/usermonx.p to $PROTOP/lib/usermon.p and edit it as you see fit.
Your $PROTOP/lib/usermon.p will not be overwritten in future updates where lib/usermonx.p will.