When I turned off the lights in the office, I locked the door and left.

以下几种表达都是正确的

【1】When I had turned off the lights in the office, I locked the door and left.

【2】After I had turned off the lights in the office, I locked the door and left.

【3】After I turned off the lights in the office, I locked the door and left.

【4】After turning off the lights in the office, I locked the door and left.

【5】Having turned off the lights in the office, I locked the door and left.

备注(1):第1/2/3为从属连词引导时间状语从句作主句时间状语。第4为介词短语作时间状语， 第5为现在分词完成体作时间状语。

备注(2):第1/2种表达等于第5种表达。第3种表达等于第4种表达。

补充一下：如果是学校考试，按胡老师的改比较稳妥。如果日常使用，好题老师的改法比较常见。但是如果只论对错的话，网友的原句并没有什么语法错误。很多同学误以为做连词的when只有“当”的含义，其实它也有after的含义，也就是说，when本身就可以表示动作的先后关系，并不一定要通过过完来体现。比如说下面这句话的when就是after的含义：

When the crude oil is obtained from the field, it is taken to the refinery to be treated

我们也可以查查朗文的解释：

只是说，在谈论过去发生的事，你可以（CAN）用过完，但不意味着你一定要用过完

一家之言，仅供参考；

勤查英英，必有所获！

When I turned off the lights in the office, I locked the door and left.

句子不对，至少不好。主要是主句动作与从句动作的先后关系没有体现出来。可以改为：

When I had turned off the lights in the office, I locked the door and left.

After I (had) turned off the lights in the office, I locked the door and left.