Does DocumentDB support ttl?

The TTL function itself is supported.
https://docs.aws.amazon.com/documentdb/latest/developerguide/best_practices.html#best_practices-ttl_timeseries

Basically, it can be used in the same way as MongoDB.
The following document describes the differences between Amazon DocumentDB and MongoDB.
https://docs.aws.amazon.com/documentdb/latest/developerguide/functional-differences.html#functional-differences.with-mongodb

Yes TTL is supported in DocumentDB and function same as it does in Mongo. Please find the following documentation around that for reference. https://docs.aws.amazon.com/documentdb/latest/developerguide/how-it-works.html#how-it-works.ttl-deletes