Downloading files on android app

[Tgill]

My colleagues and I commonly need to share files, we do so via the team chat.  These files are commonly .apk files.  When I use my phone to try and download the file, the file just downloads into the app.  The app notifies me saying download complete but when I press on it, it just launches the app.  I am wondering how I can actually download the file directly onto my device so I may use the .apk