1. My computer is crush down and I lost my previous PDF file since 2012. Is there any way I can get back from my account online?

[gemen88]

2. I purchased software for this year, is there any way I can work it in my account without download and just type license code and where I should type?

[Mike9241]

if you used online in previous years the last 6 years should be available to open and save as a pdf to your computer

if you'll be using desktop software for 2021 you must upload your 2020 tax file (ending in .tax2020) to your computer so important info can be transferred from it into your 2021 return. The best place to save it would be your desktop

open the desktop software and activate it then click on "start a new return". a window will open which will show nothing. use the "browse" feature to get to the file on your desktop. highlight the file with your mouse. then click on open. the data from 2020 should transfer to the 2021 return.

[Critter-3]

If you meant that you have been using the downloaded versions all these years then the only copies of the return were in that computer or in any backups you made ... nothing was saved online. 

Then if you are asking if you can used the activation code from the download you bought on the ONLINE program that is a hard no.  If you are going to use one of the online programs that are not free then you will have to pay for the online fee to file the return.  Get a refund of the download you cannot use.