I'm no expert on German National Socialism or Hitler, but I found somethings on communism and socialism in general.
Worth reading 1/2:
Pius IX, Nostis et Nobiscum, December, 8, 1849:
6. You are aware indeed, that the goal of this most iniquitous plot is to drive people to overthrow the entire order of human affairs and to draw them over to the wicked theories of this Socialism and Communism, by confusing them with perverted teachings. But these enemies realize that they cannot hope for any agreement with the Catholic Church, which allows neither tampering with truths proposed by faith, nor adding any new human fictions to them. This is why they try to draw the Italian people over to Protestantism, which in their deceit they repeatedly declare to be only another form of the same true religion of Christ, thereby just as pleasing to God. Meanwhile they know full well that the chief principle of the Protestant tenets, i.e., that the holy scriptures are to be understood by the personal judgment of the individual, will greatly assist their impious cause. They are confident that they can first misuse the holy scriptures by wrong interpretation to spread their errors and claim God's authority while doing it. Then they can cause men to call into doubt the common principles of justice and honor.
18. As regards this teaching and these theories, it is now generally known that the special goal of their proponents is to introduce to the people the pernicious fictions of Socialism and Communism by misapplying the terms "liberty" and "equality." The final goal shared by these teachings, whether of Communism or Socialism, even if approached differently, is to excite by continuous disturbances workers and others, especially those of the lower class, whom they have deceived by their lies and deluded by the promise of a happier condition. They are preparing them for plundering, stealing, and usurping first the Church's and then everyone's property. After this they will profane all law, human and divine, to destroy divine worship and to subvert the entire ordering of civil societies. In this critical period for Italy, it is your duty, venerable brothers, to help the faithful realize that if they let themselves be deceived by such perverted doctrines and theories, these theories will cause their temporal and their eternal destruction.
19. Therefore, warn your faithful that the very nature of human society obligates its members to obey its lawfully established authority; nothing in the precepts of the Lord on this subject, which are proclaimed in holy scripture, can be altered. For it is written: "Be subject to every human institution for God's sake, to the king as supreme or to governors as sent by him to punish wrongdoers and to praise those who do right. For it is God's will that by doing right, you should put to silence the ignorance of foolish men. Be as free men, yet without using freedom as a pretext for evil, but be as servants of God."[16] And again: "Let ever soul be subject to the higher authorities. For there is no authority except from God, and those that exist have been instituted by God. Therefore, he who resists authority resists what God has appointed, and those who resist will incur their own condemnation."[17]
20. Let them furthermore know that it is likewise a mark of the natural, and so of the immutable, condition of human affairs that even among those who are not in higher authority, some surpass others in different endowments of mind or body or in riches and such external goods; therefore it can never be lawful under any pretext of liberty or equality to usurp or injure in any way the good or rights of other men. Divine precepts on this subject are clear and can be found throughout the holy scriptures. They forbid us strictly even to desire the goods of other men, much less seize them.[18]
16.I Pt 2.13f.
17.Rom 13:1f.
18. Ex 20.45, 17. Dt 5.19, 21.