The Prophet ﷺ said: “The most beloved of your names to Allah are ʿAbd Allah and ʿAbd al-Rahman” (Muslim 2132), and scholars add to them all names formed on a name of Allah. The name al-Hadi occurs 2 times in the Quran; its page in the 99 Names section gives its meaning and verses.
ʿAbd al-Hadi joins ʿabd with al-Hadi, from the root h-d-y of guidance (huda): the One who guides His creatures to what benefits them and hearts to the truth. The Quran: “Allah guides those who believe to a straight path” (22:54). Common in the Maghreb and the Levant.
And so those who were given knowledge may know that it is the truth from your Lord and [therefore] believe in it, and their hearts humbly submit to it. And indeed is Allāh the Guide of those who have believed to a straight path.