It lets you into the country without a visitor's visa but you need to then process your work/residency visa. That takes about a month if it's not Ramadan. It's very hard to leave the country again until you have residency.

Residency is proven by a page in your passport or by a Qatari expat residency card. The two are equivalent and either valid in place of the other.

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Since Allah has given me a brain, it would seem like a sin not to use it.