ًDoes we need to find the word 'Ahmad' or its translation in New Testament to prove the truth of Quran?

بسم الله الرحمن الرحيم

 وَإِذْ قَالَ عِيسَى ابْنُ مَرْيَمَ يَا بَنِي إِسْرَائِيلَ إِنِّي رَسُولُ اللَّهِ إِلَيْكُم مُّصَدِّقًا لِّمَا بَيْنَ يَدَيَّ مِنَ التَّوْرَاةِ وَمُبَشِّرًا بِرَسُولٍ يَأْتِي مِن بَعْدِي اسْمُهُ أَحْمَدُ ۖ فَلَمَّا جَاءَهُم بِالْبَيِّنَاتِ قَالُوا هَٰذَا سِحْرٌ مُّبِينٌ (6) 

This Ayat 6 from Surah Al-Saff mentions that Isa said to Israelites: Oh the children of Israel (Yaakob), verily I am a messenger of Allah sent to you, confirmed what came before me i.e. Torah and bringing glad tiding with the arrival of a messenger who will come after me his name is Ahmad. When he came to them with proofs/miracles they said this is a clear magic. 

Injeel was given to Isa A.S.  Injeel . In Greek, this is known as Euaggelion with phonetic Spelling: (yoo-ang-ghel'-ee-on)

Strong's Greek: 2098. εὐαγγέλιον (euaggelion) -- good news (biblehub.com)

As Allah used the word "Injeel", it makes sense to believe that Injeel was revealed to Isa A.S in Greek, not in Hebrew or Aramaic. 

εὐαγγέλιον - Wiktionary, the free dictionary

Gospel is the old english translation of Injeel. 

The 4 gospels of New Testament is not the Gospel of Isa. They have unknown authors and they were written many years after Isa ascension to heaven . They are definitely not the word of God as they contradict each other in many instances.  They are different versions of the biography of Isa A.S.  Biblical scholars mentioned how the gospels are sourced from each other. 

Gospel of John reached its final form around year 90-110 AD. Again the authors are known, let alone to know whether they met Isa A.S. 

Earlier than these gospels are 13 letters written by Paul, known as epistles. These letters were wrote by a human known as Paul. The gospels undoubtedly were written after the epistles and it is very hard to say that these Pauline epistles did not influence the theology of the 4 gospels. 

And then the New Testament include  Acts of the Apostles which is an unverified history book. It speaks about the foundation of the Christian Church and the spread of its message to the Roman Empire.

And then come the Epistle to the Hebrews. This is a letter with unknown author. 

And then the 7 epistles of Catholic Church, again unknown author and finally the book of revelation which again of unknown author. 

None of these books that make up the New Testament is the word of God, but rather the authors are unknown except the Pauline epistles. 

There were many christian books not included in the book. They are known as Apocrypha. It is very difficult to know whether we can find the mention of 'Ahmad' in the bible as it is a translation, not in its original language. 

Isa A.S did say what he said about a messenger that will come after him. Unfortunately, we cannot rely on the New Testament to pass on this message as Quran never claimed this. 

I will reserve discussion on  Isaiah 42 later.