There is a memorial stone on Mexikoplatz in Vienna which looks like shown below.
The text on the stone means the following (my emphasis):
In March 1938 Mexico was the only country that officially protested in the Leage of Nations against the violent annexation of Austria by the national-socialist German Empire. The city of Vienna gave the name Mexico Square to this place in commemoration of this act.
Original German text:
Mexiko war im März 1938 das einzige Land, das vor dem Völkerbund offiziellen Protest gegen den gewaltsamen Anschluss Österreichs an das nationalsozialistische Deutsche Reich einlegte. Zum Gedenken an diesen Akt hat die Stadt Wien diesem Platz den Namen Mexiko-Platz verliehen.
In his speech on July 8th, 1991, then-chancellor Franz Vranitzky also mentioned violence during the Anschluss (my emphasis):
It is undisputed that in March 1938 Austria became a victim of a military aggression with terrible consequences.
Original German quote:
Es ist unbestritten, dass Österreich im März 1938 Opfer einer militärischen Aggression mit furchtbaren Konsequenzen geworden war.
The quote can be found in the parliamentary protocols, p. 15 (see yellow highlight in the screenshot below).
Both the lettering on the memorial stone and Vranitzky's speech can be considered official statements of the Austrian government. Both of them claim that the Anschluss involved physical (military) violence.
What are examples of acts of violence (by the Nazi Germans) that happened during the annexation of Austria in 1938? In other words: What facts can be used to support the narrative that the annexation of Austria was violent and/or involved military aggression?
Here is what I could find.
The first document that comes to mind when we talk about the Anschluss is the Moscow Declaration of 1943 which contains following statements regarding Austria:
DECLARATION ON AUSTRIA
The governments of the United Kingdom, the Soviet Union and the United States of America are agreed that Austria, the first free country to fall a victim to Hitlerite aggression, shall be liberated from German domination.
They regard the annexation imposed on Austria by Germany on March 15, 1938, as null and void. They consider themselves as in no way bound by any charges effected in Austria since that date. They declare that they wish to see re-established a free and independent Austria and thereby to open the way for the Austrian people themselves, as well as those neighboring States which will be face with similar problems, to find that political and economic security which is the only basis for lasting peace. Austria is reminded, however that she has a responsibility, which she cannot evade, for participation in the war at the side of Hitlerite Germany, and that in the final settlement account will inevitably be taken of her own contribution to her liberation.
The first problem is that here the Allies present the final results of their decision regarding Austria, but shed no light to the thought process. I could not find any mention of why they think that Austria was Hitler's first victim. Correct me if I'm wrong, but nowhere in this document I could find any statements like "the Germans killed X and wounded Y Austrians in village Z."
Furthermore, the above passage seems to contradict itself: First, they claim that Austria is
first free country to fall a victim to Hitlerite aggression,
Austria is reminded, however that she has a responsibility, which she cannot evade, for participation in the war at the side of Hitlerite Germany
Both statements are mutually exclusive. If Austria is a victim of "Hitlerite aggression", she does not have responsibility for participation in the war (like true victims of Hitler Poland or Czechoslovakia). If Austria is fully or partly responsible for fighting together with Germany, it is not its victim.
Presence of German troops
Most sources I am aware of (e. g. Britannica) claim that German troops invaded Austria during the Anschluss. However, nowhere could I find any mention of those troops exercising their military power. Rather, it looks like the Germans had weapons, but never used any of them during the annexation.
Web page of the City of Vienna claims following:
Fateful events in early March 1938
When we talk about the events in early March 1938 we remember and mourn all Austrians and all citizens of other countries who fell victim to the atrocities of the Nazi regime. Following the events on 11 and 12 March 1938 Austria lost its independence and sovereignty for seven years. March 1938 marks the onset of great suffering and the darkest chapter of Austrian history. The terror started immediately. In the first few hours after the "Anschluss" tens of thousands of people were arrested in Vienna alone. A large part of the resistance movement was eliminated right in the beginning. The first transports to the Dachau concentration camp left Vienna on 1 April 1938.
They arrived at the crack of dawn
On 12 March 1938 at 5 o'clock in the morning senior Nazi officials Heinrich Himmler and Reinhard Heydrich arrived in Vienna. Half an hour later German troops crossed the German-Austrian border and German airplanes landed at the airport in Vienna. At 4 o'clock in the afternoon of the same day Adolf Hitler arrived in his hometown of Braunau in Upper Austria, where he was greeted by cheering Austrians. The 8th German army met with great enthusiasm on its way to Vienna. The full scale of the horrors that followed the cheering was only revealed in April 1945.
I don't see any mention of Austrian resistance against German troops in March 1938.
The US Holocaust Memorial Museum makes a similar statement:
March 11, 1938
On March 11–13, 1938, German troops invade Austria and incorporate Austria into the German Reich in what is known as the Anschluss.
A wave of street violence against Jewish persons and property followed in Vienna and other cities throughout the so-called Greater German Reich during the spring, summer, and autumn of 1938, culminating in the Kristallnacht riots and violence of November 9-10.
Here, violence against Jews is mentioned. But no violent incidents involving Germans on one side and Austrians on the other are presented.
Availability of weapons
Unless I'm missing some crucial documents, it seems that the Austrians did not resist invading German troops.
An article by the Süddeutsche Zeitung supports this view:
On March 1938 the German Wehrmacht marched into Austria without resistance.
Original German text:
Am 12. März 1938 - marschierte die Wehrmacht ohne Gegenwehr in Österreich ein.
The question is: Did they not fight the Germans because
- they didn't want to, or
- because they couldn't?
Given the fact that 4 years before there was a "hot" Civil War I conclude that in 1934 there were several political parties and paramilitary organizations with enough people, weapons, and organization to engage in street fights in at least two major cities (Vienna and Linz). Assuming that these resources did not completely vanish until 1938, the Austrians should have had the ability to fight back. They probably could not win against the Germans, but they could make the annexation harder for them.
Invasion of German troops
[...] For some time Austria considered military resistance [against the Germans]. It could have had devastating consequences for the German troops. Especially in the upper Austrian region there were detailed defense plans of the Austrian army. But when German mobilization was reported [to the Austrians], the military units received the instruction by the Federal Chancellor Schuschnigg to not fire any shots.
Original German text:
Der Einmarsch deutscher Truppen
[...] Einige Zeit lang hatte Österreich militärischen Widerstand erwogen; dies hätte für die deutschen Truppen durchaus verhängnisvolle Folgen haben können. Besonders für den oberösterreichischen Raum existierten detaillierte Verteidigungspläne des Bundesheeres. Doch als am 11. März die von Hitler tags zuvor befohlene deutsche Mobilmachung gemeldet wurde, erhielten die militärischen Einheiten im Auftrag des Bundeskanzlers Schuschnigg die Weisung, keinen Schuss abzugeben.
Aforementioned Britannica article also says (my emphasis)
On March 12 Germany invaded, and the enthusiasm that followed gave Hitler the cover to annex Austria outright on March 13.
This statement doesn't jibe with the statements on the stone (violent annexation) and Vranitzky's speech (military aggression). If the Germans were violent towards the Austrians to any significant degree, there could be no enthusiasm on Austrian side.