so to use electrum i have to trust other softwares?
Exactly, only way to be 100% sure that you download correct file is to verify that file, and for that you need some tool/software. But you have possibility to check that software integrity in the way that it is described in post by
pooya87.
You do not need to install Electrum first to verify it, it is actually the opposite procedure - you need to verify Electrum files which you download before installation, because otherwise the whole procedure does not make sense.
Electrum is easy to use light desktop wallet, but as you can see it is not 100% safe, especially for inexperienced users. Does this mean that you should stop using Electrum? It all depends on you and how much you really care about your coins, and accordingly to that you can take steps to increase security of coin storage. Hardware wallets are a logical choice, for 60-70$ you can get much better security then with most desktop wallets.