Where can I find the pets I downloaded from the exchange?

Actually, I fixed the first problem. However, the problem of not being able to adopt pets in game continues. 

@Bibelotje  Are you using any mods, and does it help to remove them?  NRaas mods should be fine and not interfere, and in fact NRaas MasterController has an Adopt Pet command that can stand in for the newspaper function.  Click on the sim and select NRaas > MC > Basic > Adopt Pet if you'd like to try this.

If you'd rather not use mods, please try adopting with a different sim in the same household, and if that doesn't work (or your household only has one sim), with a sim in a different household.  You don't need to save your progress, or you can use "save as" and rename the save so the original remains intact.

Some reasons the option to adopt might not show up are that the household is already full—max eight humans or six pets, including pregnancies, and ten total—or that an existing event, for example another adoption, hasn't completed yet.  Let me know if either of these could be the case.