The answer for : Is there an free alternative for Adobe PDF, this is for you ..
To start with, you must be wondering why one should find an alternative for Adobe PDF. If you have used adobe PDF, then you will know that it takes considerable amount of time to load up completely. It consumes a lot of system resources as it uses a lot of unused plugins, which is mostly not necessary for regular use.
You’ll find a lot of alternative, free PDF readers on internet and Sumatra PDF is one of them.
Sumatra PDF is built for Windows platform and is very light weight. It’ is just about 1mb. The soul purpose of Sumatra is to read pdf files and it does it very efficiently.
The source code of Sumatra is available from the same site and you can use it to make any further enhancements or modifications as per your requirement.
I did not find concrete written information under what licsense Sumatra is distributed. If anyone has clue about this, please let me know so that I can update about the same.