All Praise be to Allah and blessings be upon the
Prophet Muhammad ﷺ.
The Qur’an which is the last and final scripturerevealed by Allah to all mankind, has always been preserved and protected throughout the ages. Allah says in the Qur’an: “Indeed, it is We who sent down the Quran and indeed, We will be its guardian.” 
This was necessary so that the state of the Muslim ummah does not become like the people before them, where the scriptures got changed and the message
got distorted. Hence it became nearly impossible for the previous nations before the Prophet Muhammad ﷺ to actually find out what the original teachings of their religion were. The following is a brief outline of the History of the Qur’an especially since the time of Uthmaan.
Before Uthmaan(May Allah be pleased with him)
When the Qur’an was revealed to the Prophet ﷺ , the Sahaba used to write it on various leaves, rocks, leathers, etc and it was compiled during the time of Abu Bakr (May Allah be pleased with him). The same mushaf was passed down to Umar and before he died, he left it in the house of Hafsa, his daughter.
During the reign of Uthmaan (May Allah be pleased with him), there were several issues which arose. Since Islam started spreading far and wide, areas like Persia, Armenia, North Africa, etc, many people who were not Arabs also started learning Arabic and to read the Qur’an.
Al-Bukhaari narrated in his Saheeh from Anas ibn Maalik (May Allah be pleased with him) that Hudhayfah ibn al-Yamaan (May Allah be pleased with him) came to ‘Uthmaan at the time when the people of Shaam (Syria) and the people of Iraq were waging war to conquer Armenia and Azerbaijan. Hudhayfah was alarmed by their (the people of Sham and Iraq) differences in the recitation of the Qur’aan, so he said to ‘Uthmaan, “O Ameer al-Mu’mineen! Save this nation before they dispute about the Book (Qur’aan) as the Jews and the Christians did before.” So ‘Uthmaan sent a message to Hafsah saying, “Send us the manuscript of the Qur’aan so that we may make copies of the Mus-haf and we will return the manuscript to you.”
As it is known that the Qur’an was revealed in Seven Ahruf. Ahruf are different reading styles or even different wordings which might have the same meaning or a similar meaning.  Hence various tribes started fighting and boasting that their Harf/style was better than the others. It also led to a lot of confusion among various people as to which is the correct Qur’an. It could also have been possible that various errors could have come into the Qur’an using the excuse that it was a variant reading.
Hence Uthmaan (May Allah be pleased with him), commissioned a committee consisting of various Sahaba and also including the Sahaba who compiled the first Mushaf like Zaid ibn Thaabit, Abdullah ibn Zubair, etc. They all came to a decision that they would uphold the Quraishi dialect. Hence they called for the Mushaf which was kept with Hafsa, and they made a copy of the Quran in this dialect. It is also said that they left out the dots and diatrical so as to accommodate the different harfs also in the Uthmaani Mushaf.
Then after the final copy was completed, several other copies were made and sent to various parts of the Muslim world and a Qari or a reciter was also sent who would read the Qur’an in the Quraishi Dialect. Moreover, it was ordered that the other copies and fragments of the Qur’an to be burned. This totally ensured that after the reign of Uthmaan, the confusion over the Qur’an was totally eliminated.
The Uthmaani Mushaf did not have any dots or any signs for the vowels. Hence, for a Non Arab it became really difficult to understand the Qur’an. So during the era of Abdul Malik ibn Marwaan , there was again a confusion about the correct reading of the Qur’an among the Non Arabs, therefore he appointed Al Hajjaj ibn Yusuf to put marks on the letters to distinguish them from others.
Al Hajjaj appointed Nasr ibn Asim al Laythi and Yahya ibn Ya’mar Al ‘Adwaani who were qualified to do this job. They also have studied under Abul Aswad al Du’li and they were successful in putting diacritical points for the first time. It was also said that Abul Aswad al Du’li is the first person to add the marks. It can be reconciled by saying that Abdul Malik ibn Marwaan was the one who made it official.
Moreover, it was he who added the dots for marking the fathah, dammah, and kasrah. Since changing the vowels changed the whole meaning of the Qur’an, it was quite incumbent for putting those vowel signs. However, the modern format of the Dammah, Kasrah, Fathah came later on. 
Decoration of the Qur’an
During the third century hijra, everyone began competing in the calligraphy of the Qur’an and the script became more and more flowery. Additionally, there were no Surah separators or Aayah separators, in the Uthmaani Mushaf, they were added for additional reading benefit. The Shaddah also was started to be used for reverberating letters.
Many Scholars during those times, had objected to these additions, however the vast majority of the Scholars were ok with it , since it did not change the meaning and it did not affect the reading at all. They were only reading aids and it only helped to improvise and secure the correct pronunciation and intended meaning of the Qur’an.
This was a brief summary of the history of the Qur’an. Although, many Orientalists and people who have studied the history of the Qur’an claim that these changes are too magnanimous to be ignored. However, adding these dots or marks or decorations have not really changed the Qur’an since the main way the Qur’an was preserved was orally and the written texts only were supplement to thousands of memorizers of the Qur’an. It only acted as a visual aid. For anyone who is familiar with the Arabic language, it would be very easy to read without these changes. Hence to claim that they changed the meaning is totally erroneous.
 Surah Hijr 15:9
 (Philips n.d., 167-173)