To find primary sources using Google, the following will work, but be sure to evaluate the website
This search will find primary source documents relating to the Berlin Wall on the internet.
Search Tip Add the phrase site:gov OR site:edu to limit your results to the domain .gov for U.S. government agencies and the domain .edu for educational institutions in the U.S, generally considered the two most reliable domains.
You may also find valuable primary source material in Google Books, which contains millions of digitized books. Books that are in the public domain may be available in their entirety; these include books published in the U.S. before 1923, but also many other works may be available due to failure to renew copyright, for instance. To find books, do a keyword, author, or title search and then click on Tools to display limiters. To find entire books that are available for free, choose Free Google ebooks.