I don't think I understand the problem. Is it linked in a web page? If so, just click on the link. That will save it in the Download directory, where you can find it (and install it, if you want) with a tool like OI File Manager or some other file browser.
I’ve looked at a lot of different solutions, and in my humble opinion Aspose is the way to go. Here’s the link: http://aspose.com
subject: How download a apk file from internet with my android app ?