Where to find it when it was downloaded
If you have been able to "download" the file, the most likely location to find it is either
It wasn't downloaded, but "saved for offline reading"
But as it turns out, the stock browser didn't give you that option, and you had to "save for offline reading" -- which is something different. In this case the file probably is stored on internal storage (below
/data/data/com.android.browser). Without root you've got not many chances to access it there. So you could either try with a different browser -- or simply copy-paste the text file into some note-taking app / editor (e.g. Jota Text Editor or AmbleLink Notepad Basic Ed.).
Alternative download options
If you have to do this more often, or formatting gets lost on copy-paste, you're probably much better of with some "downloader tools". I just know about Tasker, which offers
HTTP_GET actions. Depending on your ROM, the shell might provide
wget (stock ROM on my Milestone 2 had this), so all you need in that case is a terminal app (e.g. Android Terminal Emulator), and there simply execute
# change to the directory where you want to store the downloaded file in
# get the file
Adjust that to your needs, of course :)
Special downloader apps
Other alternatives would include special "Downloader Apps", like e.g. Download All Files or Easy Downloader, which you might want to give a try.