Yes Pyrex is freezer safe and can be put in the freezer to store food in.
You can place Pyrex in the freezer but first make sure that the Pyrex is cooled down before you freeze it.
if you put the hot Pyrex into the freezer right after taking it out of the oven then the Pyrex when hot can crack or shatter because of the hot to cold shock.
As long as you allow the Pyrex to cool down before placing it in the freezer the Pyrex will be safe to store in the freezer.
Also if you store food in Pyrex in the freezer you should allow the Pyrex dish to set out for 30 minutes so that it warms up some before you put it in the oven.
If you take the Pyrex directly out of the freezer and put it right into the oven then the thermal shock from sudden temperature change can also shatter the Pyrex.
As long as you use the Pyrex correctly it's safe to use in the microwave, oven, freezer, refrigerator etc.