How to download a .zip attachment returned by an HTTP API call and parse it in webMethods?

I’m developing a webMethods service where I’m calling an API via pub.client:http, and the output expected is a .zip file (having data in JSON format) which I need to download, parse and store some data in a DB. When I use pub.client:http, I’m getting bytes and stream as output. I’m able to convert the bytes to a string using pub.string:bytesToString, and see the JSON data as expected in the file. But I’m not sure how to convert the data to a document format. When I try pub.document:bytesToDocument, I don’t see any output returned. Can someone help?
Also, I was expecting the API to return an attachment that would need to be downloaded. Can someone suggest how to download an attachment in webMethods returned by an API?