If you tell me you are looking for (e.g., al-Būnī, Ibn ʿArabī, Faḍl Allāh al-Ḥurūfī, or a modern study by Toufic Fahd), I can give you more precise search directions.
It seems you are looking for a on ʿIlm al-Ḥurūf (the “science of letters” or Arabic letter mysticism, often associated with esoteric traditions like ḥurūfiyya , Sufism, and Kabbalistic-influenced Islamic occult philosophy). ilm al-huruf pdf