Mahatma Gandhi's view on religious conversion is documented at this url:
In his letter to Premaben Kantak, 22-4-1932 he wrote (http://www.mkgandhi.org/ebks/Gandhiji-on-Religious-Conversion.pdf):
"Regarding conversion, I don't mean that it is never justified. But no one should invite another person to change his or her religion. When, however, a person has changed his religion under compulsion or in ignorance, there should be no objection to such a person rectifying his error, that is returning to his original religion, on the contrary, he should be encouraged to do that. His action is not conversion.
Gandhiji's views from Bihar notes (8-10-1925) indicate that:
"Christian missionaries have been doing valuable service for generations, but in my humble opinion, their work suffers because at the end of it they expect conversion of these simple people to Christianity ...How very nice it would be if the missionaries rendered humanitarian service without the ulterior aim of conversion."
Gandhiji wrote a letter to the Christians of Kerala, which was published in Harijan, 30-1- 1937:
"Why should a Christian want to convert a Hindu to Christianity and vice versa? Why should he not be satisfied if Hindu is a good or godly man? If the morals of a man are a matter of no concern, the form of worship in a particular manner in a church, a mosque or a temple is an empty formula, it may even be a hindrance to individual or social growth and insistence on a particular form or repetition of a credo may be a potent cause of violent quarrels leading to bloodshed and ending in utter disbelief in religion, i.e., God Himself."
(Young India: August 8, 1925):
As I wander about through the length and breath of India I see many Christian Indians almost ashamed of their birth, certainly of their ancestral religion, and of their ancestral dress. The aping of Europeans by Anglo-Indians is bad enough, but the aping of them by Indian converts is a violence done to their country and, shall I say, even to their new religion.
(Harijan: March 13,1937)
My fear is that though Christian friends nowadays do not say or admit it that Hindu religion is untrue, they must harbour in their breast that Hinduism is an error and that Christianity, as they believe it, is the only true religion. So far as one can understand the present (Christian) effort, it is to uproot Hinduism from her very foundation and replace it by another faith.
(Harijan: April 3, 1937)
"When the missionary of another religion goes to them, he goes like a vendor of goods. He has no special spiritual merit that will distinguish him from those to whom he goes. He does however possess material goods, which he promises to those who will come to his fold."
(Harijan: November 5, 1937)
"Only the other day a missionary descended on a famine area with money in his pocket, distributed it among the famine stricken, converted them to his fold, took charge of their temple and demolished it. This is outrageous."
(Young India: April 23, 1931)
"I hold that proselytizing under the cloak of humanitarian work is unhealthy to say the least. It is most resented by people here. Religion after all is a deeply personal thing. It touches the heart. Why should I change my religion because a doctor who professes Christianity as his religion has cured me of some disease, or why should the doctor expect such a change whilst I am under his influence?"