Did priests do this/allow this:

• - Show Christian movies in Churches? (with projector screen)
• - Hold Catholic seminars in Churches?
• - Graduation ceremonies in Churches?
• - Hold Church fundraisers in Churches?

Or was the Church building for Catholic worship only?

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Ideally the Church proper should be used only for Mass and religious ceremony, such as Baptisms, Rosary, Stations of the Cross, Benediction, Vespers, Holy Hour, Confessions, that sort of thing. Conferences, fund raisers, Legion of Mary, Catechism classes, graduation ceremonies, Christian movies (with screen), pancake breakfasts and the like would be held in the Parish Hall. Well, what if you don't have a parish hall, and it's raining outside?
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Bottom line, you can do any of these things inside the Church proper when you don't have any alternative place to go, but you must remove the Blessed Sacrament from the tabernacle, and it's a good idea to leave the door open so everyone can see that the tabernacle is empty, such as on Good Friday when you use the Altar of Repose. Only this time you don't use the Altar of Repose, you take the Blessed Sacrament out of the building entirely and use another secure location. This might be a difficulty for the priest.
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When a new parish is being built, the first building used for Mass is constructed in an off-center place where it can eventually be used as a parish hall after the permanent Church is established. One building project at a time, as the funds can be collected and saved up. A growing parish presents a lot of challenges for the pastor and the faithful. This is all inherently part of Catholic tradition.
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After the novelties following Vatican II, when the tabernacle was moved away from the center of the main altar, this invited other innovations. When Our Lord is in exile every day as a matter of course, people forget to genuflect, and that's seen as an accommodation to help Protestants feel better coming inside for whatever reason, like a funeral or a musical program or a wedding. So that's all part of the revolution of Newchurch, and a different topic as it were. That is, I'm not sure if you're asking about that.
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saintsoaring - I am pretty sure that back in the middle ages/early renaissance when churches were quite large and did not always have pews, they used churches for more than just prayer.  I think they held gatherings of sorts.  However, back then there was such a thing as a sanctuary, and that was certainly not profaned in such gatherings if they took place.  

Before Vatican II, I remember the parish churches using the church for the parochial 8th grade graduation ceremonies. The graduates processed into a quiet and somber church and a brief prayer was read over them, then the pastor gave a rather lengthy sermon urging the graduates to be faithful to the Holy Faith. The entire ceremony took less than 30 minutes.  For the ladies, all dressed in white like brides, it was the first time many wore their first pair of high heels, so they wobbled up the aisle.  For the guys, it was the first time that we saw them in a proper suit and tie. I do not remember any graduation certificates being handed out, but after the graduation ceremony, the graduates and parents went into the classroom and were served refreshments. While the girls abstained from the cookies and cakes in an effort to trim off pounds for the summer months, the young men took double or triple portions and then looked for more. They had bottomless legs.

Catholic High Schools had two ceremonies as did the Catholic colleges. The first ceremony was in church where prayers were read over the graduates and sermon(s) were delivered. The dress was formal. The second ceremony, which involved caps and gowns, was generally held in the auditorium, in the football field, or at a public venue.

I have never heard of showing movies in Churches before Vatican 2.

I have never heard of pre-Vatican 2 pastors holding graduation ceremonies or Church fundraisers in the Church, though I would not doubt that parishes might hold a votive Mass on the occasion of the graduation from the parish school--but I doubt they actually handed out diplomas, etc.

As for "Catholic seminars", if you're talking about a mission where a priest comes in to preach, I have heard that this was done in pre-Vatican 2 Churches.  If you're talking about some other kind of seminar, I'm not sure what you are describing.

The Redemptorists were founded with this charism in mind.

I would say No to all four questions; and when we talk of missions I believe they a form of religious instruction, part of a more extensive time of prayer and spiritual refreshment, and renewal of faith. These were regarded as a Church service, not a conference.

In a pioneering situation churches may have been used for parish activities other than prayer, but only if there was no alternative.

I recall BF giving a conference from the Sanctuary in St John's Church in Dun Laoire a number of years ago.

Did priests do this/allow this:

• Show Christian movies in Churches? (with projector screen)
• Hold Catholic seminars in Churches?
• Graduation ceremonies in Churches?
• Hold Church fundraisers in Churches?

Or was the Church building for Catholic worship only?

I guess it depends on how far back in history you want to go.
Pre-reformation in England, for instance, the nave of a church was considered to belong to the laity, and it was used for all sorts of non-religious purposes on a daily basis. There are records showing that people used to light fires and cook in the nave of old St. Paul's Cathedral in London. Lawyers used it as a place to meet their clients, and scribes sold their services from booths set up along the outer walls.
In country parishes, the church was often the only building of substance in the area, and was used for council meetings, as a courtroom, for plays, and 'church ales' were a regular occurrence for fund-raising purposes.
Of course, all of this went on at a time when churches had a rood screen in place to separate the nave from the sanctuary and the altar. The laity were never allowed beyond the rood screen.