Sorry, but I don't seem to understand your problem, could you please give more details? And what browser and what program are you using to open the files?
upto this, the main should be stopped until PDF file gets fully downloaded. How to fix it?
If the PDF was saved using "Optimize for fast web view" then it will open to the first page immediatly as it downloads the rest of the file. So, it's different from one PDF to another.
As far as how long it took you to download the entire PDF, there's nothing in Reader that will help you with that.