I won't bore you with the "why", but suffice to say there are certain situations where it is useful to have the contents of a file contained in a macro. Obviously don't read a multi-Gb file into a macro, it might struggle.
Here's a process to do it.
It's very simple in fact. The trick is to use the "Read Document" operator followed by "Documents to Data". This has the effect of reading the entire contents of a file into a single named attribute in a one row example set. This by itself is useful but from there, it's a simple matter to use "Extract Macro" to make a macro equal to the value of the attribute for the single row.