The Gemara in Masechet Gittin discusses the Halacha which forbids writing only a portion of a book of the Tanach. If one is writing a portion of the Tanach, he must write the entire book. However, the Gemara adds, as it became difficult for congregations to have complete scrolls of all the books of the Prophets, the Sages enacted a special provision allowing the writing of a Sefer Haftarot – a parchment scroll containing all the Haftarot, which would be used for the Haftara readings throughout the year.
It seems clear from the Gemara that the Haftara must be read from a parchment with the text written in the special ink, like our Sifreh Torah. On this basis, the Aruch Ha’shulhan (Rav Yechiel Michel Epstein of Nevarduk, 1829-1908) supports the view of the Lebush (Rav Mordechai Yaffe, 1530-1612) that the Haftara must be read from a parchment scroll, like the Torah reading. The Lebush questioned the common practice to read the Haftara from printed books, and several other Aharonim, including the Elya Rabba and the Rama, concurred and required the use of parchment scrolls. The Aruch Ha’shulhan noted that indeed, the custom in Lithuania was to have complete parchment scrolls of each book of the Prophets – a complete Book of Yeshayahu, a complete book of Yirmiyahu, etc. – which were used for the Haftara readings. At very least, the Aruch Ha’shulhan writes, congregations should have a Sefer Haftarot – a parchment scroll containing all the Haftarot.
Hacham Ovadia Yosef discusses this question in his Yehaveh Da’at (5:26), and concludes that it is, in fact, proper to use a parchment scroll for the Haftara. If a congregation does not have a parchment scroll, then it is preferable to use a complete printed Tanach, rather than read from a printed Humash or from a printed Haftara book.
Hacham Bension Abba Shaul (Israel, 1923-1998) noted that if a congregation has a special Hafara scroll, it should not be kept together with the Sefer Torah in the ark, as they are on different levels of halachic sanctity. Many synagogues keep the Haftara scroll together with the Sifreh Torah, but this is incorrect. The Haftara scroll should be kept in a separate closet, or somewhere next to the Hechal, but not in the Hechal together with the Torah scrolls.
It should be noted that in synagogues which follow the custom of bringing the Haftara book to the Teba together with the Sefer Torah, there is no need to open the Haftara book and show the congregation the text, as is customary to do with the Sefer Torah. The Haftara book should remain closed until it is read. There is no value in showing the congregation the text as there is with the Sefer Torah, and doing so gives the appearance of equating the Haftara book with the Sefer Torah, which is inappropriate.
Summary: It is preferable for synagogues to read the Haftara from a parchment scroll. They should either have a separate scroll for each book of the Prophets, or have one scroll containing all the Haftarot. If a congregation does not have a parchment scroll, the Haftara should be read from a complete printed Tanach. If a congregation has a special Hafara scroll, it should not be kept in the Hechal together with the Torah scrolls, and it should not be opened and shown to the congregation before it is read, as is customary to do with the Sefer Torah.