A formal contract is signed which is renewable annually.

签署的一份正式合同每年可续签一次。

《柯林斯英汉双解大词典》

My idea is that we should sign a formal contract.

我认为我们应该签订一份正式的合同。

youdao

We hurried an oral agreement before signing a formal contract.

在签正式合同之前，我们先草签了一份口头协议。

youdao

American opposition or not, the IPI project seems to be headed for a formal contract signing this summer.

FORBES

Originally a letter of intent, the agreement to supply 200MW to the Tokyo Electric Power Company (TEPCO) is now a formal contract.

BBC: Japan earthquake power supply deal nets Aggreko ?60m

Esa is expected to sign a formal contract with Astrium (Bremen, Germany) in the coming days to lead the production of the service module.

BBC: Europe and US agree details for Orion astronaut spacecraft