You ever find an author and think to yourself “I want to read everything they have ever written”? I have that quite often, and want to add their texts into my personal search archive.
Welcome @robhaisfield
This really depends on the specific site. There isn’t a global get blog posts of Jim Neumann as PDF command. 
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Something similar has been asked here before some weeks ago. Maybe that thread can give you some ideas.
I suggest using a command line tool like curl or wget for a task like that.
Alternatively, it might be feasible with DT’s download manager.