We believe the Holy Prophet Muhammad (sa) is the last
law-bearing prophet as well as the greatest and the best prophet of Allāh. He predicted in very clear words the coming of a prophet in the Latter Days who would indeed come after him as subordinate burooz, who would serve his cause. That prophet has already come in the person of Hazrat [i.e., His Holiness] Mirzā Ghulām Ahmadas of Qādiān, India and he established the International Ahmadiyya Muslim Jamā‘at. He did not abrogate a single law of the Holy Qur’ān nor did he add anything new to it, and he came exactly according to the criteria set forth in the Holy Qur’ān.
For information about the claim of Hazrat Mirza Ghulam Ahmad (as) please refer to the book
A Misconception Removed by Hazrat Mirza Ghulam Ahmad (on whom be peace).
For books on the word "Khatam" and it's meanings check out this google drive compiled with work on this topic
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Click here to access it <