One option is to use Family Tree Maker, which syncs with Ancestry. It populates some of the metadata into your FTM database. I use and like FTM but I never use this function. Why? Because I don't like how it does citations and it chose fact categories different from what I wanted. While this doesn't download the actual document file, it does give you some metadata.
Otherwise, you need to do this manually. I've been doing this for years and it works well. I also put in every fact and citation manually. But that's me.
Part of what you can do is to cut and paste the transcribed data from Ancestry's page for it. Every Ancestry document has this data in a separate page. Then some documents also have a scan which can be downloaded. I put the full cut and paste into the citation (this is easy in FTM) or I do my own transcription if there is a scan. This carries over to every use of that citation so I only have to do it once per document.
When you download a scan you have to manually name the file.
When you download a scan, you have to separately deal with the transcribed data.
If you choose "download" on a multi-page document, it only downloads the page you're on.
Ancestry deliberately makes it difficult to download their data.