The US and UK national archives do not appear to have digitized versions of a signed copy online of the Dönitz memo authorizing Keitel et al to sign the surrender in Berlin. Since the US national archive includes a digitized signed copy of the earlier Dönitz memo authorizing Jodl to sign the surrender at Reims, this suggests the following possibilities:
- There was no signed copy from Dönitz authorizing Keitel et al to sign the surrender instrument in Berlin (this does not seem likely, and circumstantial evidence suggests this is not the case);
- There were multiple signed copies, one for each Allied power represented at the surrender ceremony in Berlin, but the US and UK either lost or did not include them in their archives (this also does not seem likely, again with contrary circumstantial evidence);
- There was only one signed original, current location in another archive but undetermined at present (this seems most likely based on circumstantial evidence, with the original probably in Russian archives).
1. There was no signed copy from Dönitz authorizing Keitel et al to sign the surrender instrument in Berlin.
This possibility does not seem likely, in fact there is circumstantial evidence to the contrary. Jodl had signed authorization from Dönitz to sign the surrender in Reims. A digitized copy of this signed memo from Dönitz is available in the US national archives (see below). To provide signed authorization for the surrender ceremony in Reims, but not for the surrender ceremony in Berlin would be inconsistent and illogical, not to mention a breach of standard practice.
Signed Dönitz memo authorizing Jodl to sign the instrument of surrender to the Allies in Reims.
Source: US National Archives
To the best of my ability, here is a translation of this authorization document into English (anyone please improve if you can):
Headquarters 6 May 1945
I authorize Colonel-General Jodl,
Chief of the Wehrmacht Command Staff in the Wehrmacht High Command,
to conclude an armistice agreement with General Eisenhower's headquarters.
[seal] [signed] Dönitz
This signed memo, in the US national archives, from Dönitz authorizing Jodl to surrender in Reims is both a documented precedent for and circumstantial evidence of also providing a signed memo authorizing Keitel et al to surrender in Berlin.
2. There were multiple signed copies, one for each Allied power represented at the surrender ceremony in Berlin, but the US and UK either lost or did not include them in their archives.
This possibility also does not seem likely. The Allies were meticulous in establishing and maintaining records and documentation (as evidenced in the amount of and nature of documentation found in their national archives). It is possible the US and UK have signed copies but have simply not digitized them for inclusion in the rest of the digitized record they have made available concerning the surrender of Germany to the Allies, but again circumstantial evidence suggests that if a signed version was available to the US and / or UK, it would appear in the archives along with all the other signed surrender documents. Why include an unsigned copy in the US national archives if the US has a signed copy available?
The US and UK national archive copies of the document from Dönitz authorizing Keitel (Army), Friedeburg (Navy), and Stumpf (Air force) to sign the Allied instrument of surrender on behalf of the government and military of Germany are included in the surrender document files without Dönitz's signature. The link on the OP's Question shows the US national archive version (see below):
Copy of Document from Dönitz authorizing Keitel, Friedeburg and Stumpf to surrender to the Allies
Source: US National Archives
Here is the copy in the UK National Archives:
Transcript of Document from Dönitz authorizing Keitel, Friedeburg and Stumpf to surrender to the Allies
Source: UK National Archives
To the best of my ability (with excellent help from LangLangC - thanks!) here is a translation of this document into English:
of the Wehrmacht [Armed Forces / Military]
Headquarters, the 7th May 45
/Please give the answer with the preceding
"business signature" (signature) from above, the date and
indicate short content. /
General Field Marshal Keitel
as Chief of the High Command of the Wehrmacht and Commander-in-Chief of the Army,
General Admiral von Friedberg
as Commander in Chief of the Navy,
as representative of the Commander-in-Chief of the Luftwaffe
to ratify the unconditional surrender of the German forces
to the Commander in Chief of the Allied Expeditionary Force
and the Soviet - High Command.
Since the version of the documents in the US national archives has signatures on all the surrender instruments, it is reasonable to assume that if there was a signed version available of the Dönitz authorization memo available to the US, the US national archives would have included it with all the other signed documents. Neither the US nor UK archives exhibit a signed version.
In looking through other sources, I also checked Wikisource and iBiblio, which both have transcripts only (and no English version of the Dönitz authorization memo).
3. There was only one signed original, current location in another archive but undetermined at present.
Having ruled out possibilities #1 and #2 (through circumstantial evidence, not documentary proof), this leaves #3 as a possible answer. But in which other archives might the signed authorization memo to Keitel et al be?
The Bundes-Militärarchiv archive copy of surrender documents provided in the link in LangLangC's answer is a fantastic find (+1 from me) but it does not contain a copy of the Dönitz authorization memo requested in the question. If there is a copy in archives in Germany, perhaps there is another source to investigate (?)
The next place to look (which I have not been able to research) would be Russian archives. Perhaps another researcher here on H:SE can turn up something there. This seems the most likely place where the signed original would be. The handwritten note in Russian at the bottom of the transcribed copy of the Dönitz memo to Keitel et al in the US national archives presents a clue to this effect.
In an earlier comment from Roman Pokrovskij and also a comment from jmstr the Russian text at the bottom of the US copy reads
«Верно / Сосновский»
which jmstr translates as
"Correct / Sosnovskij"
This suggests the Soviets had (and retained) an original (likely signed) version which they provided to the other Allied powers present in the Berlin signing (Berlin being under Soviet control). The Allies transcribed it and the Russians checked and verified their transcriptions as evidenced in the US national archive digitized copy shown above.
All of this circumstantial evidence suggests Possibility #3 as the most likely answer, with the original most likely being found somewhere in a Russian archive.
A Report of the Surrender in Berlin
In closing, I found a digitized copy of the May 10, 1945 edition of the Santa Cruz Sentinel, Volume 90, Number 112 in the University of California-Riverside's California Digital Newspaper Collection, and the lead on Page 1 under the headline Victory Guns of Moscow Thunder as Stalin Tells Of Surrender By Germans which reads, in part, as follows (note at the end of the quote that Zhukov and Tedder ask Keitel if Keitel has a copy of the surrender document to be signed, is aware of its significance, and if the German supreme command (Dönitz) agrees that it be signed - they do not ask if there is any signed authorization from Dönitz to do so, only if Dönitz agrees that it be signed):
The final act in Germany's capitulation took place in the main hall of the German military academy of engineering at the corner of Friedrichstrasse and Rheinsteinstrasse in ruined Berlin at 12:45 a.m.
There Marshal Wilhelm Keitel, supreme commander of the German armed forces; Gen. Admiral Hans Georg Friedeburg, commander of the German navy, and Col. Gen. Hans Stumpf, chief of the Luftwaffe, ratified the articles of surrender.
Marshal Gregory K. Zukov signed for Russia and Air Chief Marshal Sir Arthur William Tedder, deputy supreme commander, for the Western Allies.
Gen. Carl A. Spaatz, commander of the American strategic - air forces in Europe, and Gen. Jean de Lattre de Tassigny, commander in chief of the French army, were present as witnesses.
Radio Moscow, broadcasting a description of the surrender scene, said Keitel was flushed and his eyes filled with tears as he rose and strode to the table to sign the surrender articles.
Zhukov and Tedder entered the hall of the military academy exactly at midnight last night, the broadcast said. The Allied delegates sat in a row beneath their national flags.
Members of the Allied delegations and Soviet commanders who participated in the capture of Berlin sat at a central table, while the table for the German delegation was at one side.
"Gentlemen." Zukov said, "We are gathered here to accept the unconditional surrender of the German armed forces. I propose to come straight to business and invite the representatives of the German army."
Keitel, Friedeburg and Stumpf entered with their adjutants at 12.08 a.m.
"We are about to sign the act of the surrender of the German army," Zhukov said. "Are you in possession of the act, are you aware of its significance and is the German supreme command in agreement that such an act be signed?" Tedder asked the same questions.
"Yes," replied Keitel.
It does not appear, based on that exchange, that a signature from Dönitz was requested, only verification from Keitel that Dönitz approved.
This may not be satisfactory as a complete answer. Perhaps Russian archives will yield definitive results.