we are 2 people travelling austria between 8-15 of july 2022, we will be visiting vienna,hallstat,salzburg, saalbach,and tirol.
we were wondering if the eurail 1 month pass is good for those destinations and is it valid for all bus/train companies
*we might be using transport for only 3-4 days
Valid on trains yes but not on Buses 
maybe you buy a flexipass with 4traveldays in a month 
or a OneCountryPass Austria or the European EastPass which work out cheaper for you.
Depends on how many trips you intend to make-but as you say 1 month I would suggest looking into the REGIonal offers that are often much cheaper and do allow all normal transit IN that region only-on some weekends its even cheaper (f.e. dayticket for either Steiermark or Kärnten for just 11€).
Prebook longer trips-likely you will also have prebooked HTLs etc. for lower advance price.
In holiday areas many HTLs give out free local buspasses to their guests
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