Adolf Hitler and Adoption
Among documents reportedly seized from Hitler's Munich home after World War II is a curious paper, apparently emanating after 1940 from the Gestapo. It suggests that he was the illegitimate child of his mother and had been adopted by Alois Hitler, his mother's husband; and it mentions that a file of supporting documentation held by the Konrad Pracher family of Graz had been seized.
As far as I can tell, these documents have not come to light, and no other source I have consulted credits the story. If it were true, the Nazis would certainly have done all in their power to suppress it and destroy any documentary evidence.
The source reference given below is in general suspect, although I have no particular reason to doubt the particular paragraph where this is mentioned. Its author, David Irving, is a notorious anti-Semite, who denies Hitler's part in the Holocaust. I include this entry solely in the interests of comprehensiveness.
Microsoft Encarta 98 Encyclopedia, 1993-97 Irving, David. "Hitler's War: An Introduction to the New Edition." Available at: www.codoh.com/irving/irvhitwar.html