Is it Fard (necessary) to follow a Madhab?

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

The Islamic Fiqh passed several stages and phases, during which schools of thought arose at the beginning of the second Hajri Century. In that stage, many eminent Fuqahaa (pl. of Faqih: a scholar in Islamic jurisprudence) emerged and established schools of thought.
The most well-known of these Fuqahaa are the four schools of thought that were named after their founders. These schools produced an important positive effect on the development and progress of the Islamic Fiqh.
Many distinguished Fuqahaa followed these schools of thought. For sure, the four schools of thought do not constitute forms of partition or separation in Islam, nor a new legislation. They are, in fact, human approaches aim to understand Shari'a, manners of interpreting the Qur'an and Hadith, methods to deduce ruling from Shari'a sources: The Qur'an, Sunnah, consensus of Muslim scholars and juristic reasoning by analogy.
These schools of thought are:
1) al-Hanafiyah, named after Imam Abu Hanifa al-Nu'man (may Allah's Mercy be upon him) 80-150, A.H.
2) al-Malikiyah, named after Imam Malik Ibn Anas (may Allah's Mercy be upon him) 93-179, A.H.
3) al-Shafi'iyah, named after Imam Muhammad Ibn Idrees al-Shafi'e (may Allah's Mercy be upon him) 150-204, A.H.
4) al-Hanbaliyah, named after Imam Ahmad Ibn Hanbal (may Allah's Mercy be upon him) 164-241, A.H.
As a rule, it is not obligatory for a Muslim to follow a specific school of those mentioned. But, a Muslim has to follow the Qur'an and Sunnah and has to follow the clear sound evidence. In other words, it is not allowed to neglect the evidence (i.e. from the Qur'an or sound Sunnah) and follow the saying of any Imam, even the Imams do not follow their opinions if there is another evidence. In addition, all justifications and reasons are refuted if there is evidence in the Qur'an or proved evidence in the Sunnah.
Allah knows best.