It is customary to read the Song of Songs on the first night of Passover at the end of the Seder. In the Diaspora, where the Seder is repeated on the second night of Passover, the reading of this book is sometimes spread over the two nights, but it is more common for the whole book to be completed on the first night.
In Ashkenazic communities, the Song of Songs is read publicly on Shabbat Chol HaMoed, before the reading of the Torah. In some communities it is read from a scroll, hand written on parchment, and the reader recites two blessings: " . . .Who has commanded us to read the Megillah" and Shehecheyanu, but in many places it is read from a printed book without a blessing, each person reading it for himself.
Not only is there a mention of Pharaoh in this book but its contents are symbolic of the four different exiles and Israel's redemption from each one.
The Zohar tells us that Song of Songs embodies the entire Torah, the story of the exile in Egypt, and the redemption of Israel from there, as well as from the other oppressors, so that by reading it we are enhancing the mitzvah of recounting the story of the Exodus.
Another reason for reading Song of Songs that Passover is a time of love between G-d and Israel, who entered into a covenant and became betrothed to Him through the Exodus from Egypt [see Ezekiel, 16].