I guess it is possible to run the whole user guide in offline mode like on the good old times 20years ago with modem connections that cost money by the minute.
But is this problem reading it on a screen (I doubt it since everything gets a very much more worse formatting when not on actual screen) or reading it offline while configuring the router?
If the the problem is the offline access while configuring the router my recommendation is to use a secondary internet connection/router.