is there a rule for the size of the page file on dedicated sql server servers?
should I really disable the page file? and reduce it to 8 GB?


It isn't talking about disabling the page file - it is referring to disabling the auto-size settings.


  is there a rule for the size of the page file on dedicated sql server servers?


There are a great many, often contradictory, rules-of-thumb for the size and location of page files under various scenarios so the question will probably get closed as "opinion based" soon.

A few of my thoughts:


You certainly shouldn't turn of the page file completely.
If you have disk space issues on C: and can't grow C: then saving 24G this way would be useful to you. As an alternative to dropping the swap space completely you could move it to another drive?
Of course you probably don't ever want the machine using 8Gb of swap space, let alone 32. By that point the IO from swapping pages is going to be significantly slowing down the server, it'll have probably have ground to an effective halt before you even get close to 32Gb (at which point you have as much swapped out as in physical RAM).
If the machine is doing nothing except running SQL Server, then you should have the memory settings for the SQL instance(s) set such that it won't exhaust RAM ever. There will still be a little swapping out to the page file as the OS will prefer to page out bits of itself &amp; other services that aren't touched, to favour file cache &amp; buffers for things that are occasionally accessed.