From few months I have been reading/listening 'Durga Kavach' / 'Bhagavati Strota' / 'Siddha Kunjika Strota'. I was aware of that there is a vedic book for Devi. So I decided to explore that too, ie. Durga saptashati, after watching few videos on youtube and internet research I came to know that it was written by Markandeya Rishi, and this book contains 700 shlokas which includes mantras for Maran, Mohan, Sthambhan, Ucchatan, Vashikaran etc. (Almost all the tantra practices)
I also got to know that Durga Saptashati is Kilit which means it is kind of locked with some mantra and in order to get the benefits of recitation, we have to do the Utkilan before reading that book.
My doubt is what are bijaksharas, and how by just reciting the mantras one can attain the siddhis (maran, mohan etc).
I have also checked this link : Source