How to get doom 1 sourceport for custom maps?

I have searched for doom 1 that is not shareware because it doesn't work when i use shareware, where do I find it?

You can get doom 1 on steam and gog.com platforms or get it from original cd or floppy. And when extract(copy and paste) doom.wad to source port folder of your choice. 

Thanks i'll try that.