Assalamualaikum,Im from India, many people here when they wore new clothes or new shoes say Assalamualaikum to others like who ever is present at home that time, apart from saying dua for wearing new clothes or new shoes and others who saw him/her saying dua to him/her. Is it an act of bidah?

All Perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as that of his family and all his companions.

It is recommended for the one who puts on a new dress to name the garment and then recite one of the supplications that are reported from the Prophet . Among those supplications is what is narrated by Abu Daawood, An-Nasaa'ee, and At-Tirmithi who graded it as sound from Abu Sa’eed who said: "Whenever the Prophet got a new garment, he would name it, whether a turban or a shirt or a cloak, and then he would say: "O Allaah all praise and thanks are due to You. You have given me this garment. I seek from You its goodness and the goodness for which it was made and I seek Your refuge against its evil and the evil for which it was made." Another narration from 'Umar reads that the Prophet said: "If anyone who puts on a new garment and says: "Praise be to Allaah Who has clothed me with something to cover my nakedness and to adorn myself in my lifetime," then takes the old garment and gives it as charity, he will be in Allaah's protection and guardianship both in this life and when dies." [At Tirmithi, Ibn Maajah, and Al-Haakim]

Imaam Ahmad and At-Tirmithi reported from Mu'aath bin Anas that the Prophet said: "If anyone wears a new garment and says, 'All thanks and praise are due to Allaah, Who clothed me and gave me sustenance, whereas I have no power or strength,' Allaah will forgive all his previous sins." [At-Tirmithi]

If one sees someone wearing new clothes, it is recommended for him to say  as reported from Ibn ‘Umar that the Prophet saw 'Umar wearing a new garment and said: "May you wear new clothes and may you live nobly and die as a happy martyr.” [An-Nasaa'ee, Ibn Maajah, and Ibn Hibbaan]

As for greeting after wearing a new garment if it is practices as merely a tradition then there is no harm. If it is done as a religious act and believing that it is a Sunnah, then it is an innovation as there is no basis for that in the Sunnah according to our knowledge.