To be glad is more informal. To be pleased is more formal.

It is used both formally and informally. It could be used by a president welcoming an honoured guest: "I am so glad you are with us here this evening" and it could be used by a mother welcoming her young daughter's friend to the house: "I am so glad you came!" or by a child welcoming her friend: "Sara, thanks for coming, I am so glad to see you here!" You can also say "I am glad it did not rain today", "I am glad that the train was not late", "I am glad to know you".

Beautiful Psalm! : )

There are different perspectives on "glad" and the word is not necessarily "less formal". See this passage from the Bible that has inspired an anthem, "I Was Glad", and a hymn, "Jerusalem", both of which were sung at the wedding of Prince William and Kate Middleton. Psalm 122  1 I was glad when they said unto me, Let us go into the house of the Lord. 2 Our feet shall stand within thy gates, O Jerusalem. 3 Jerusalem is builded as a city that is compact together: 4 Whither the tribes go up, the tribes of the Lord, unto the testimony of Israel, to give thanks unto the name of the Lord. 5 For there are set thrones of judgment, the thrones of the house of David. 6 Pray for the peace of Jerusalem: they shall prosper that love thee. 7 Peace be within thy walls, and prosperity within thy palaces. 8 For my brethren and companions' sakes, I will now say, Peace be within thee. 9 Because of the house of the Lord our God I will seek thy good. King James Version (KJV)