It appears Google have made this very difficult, I guess to stop the accidental creation of various versions of documents.
If the file is a Google format, you can open it and select File → Make a copy to duplicate it.
If it isn't, the only work around I've seen within the web interface is this cumbersome solution. (Only for files smaller than 25Mb.)
See this: Blogger Help: Import and export blogs
To make a copy of your blog's posts and comments, you have to export your blog and then import it to another existing blog.
Export Your blog
To export your blog, simply click "Export Blog" from the Settings |
Then, click the Export Blog button. Your blog will be stored as a
Probably you found a solution by now, but here is a script which scans for "?" after a / in case you saved it across multiple social media channels: