i am using Draftsight 2015x64SP2

i get the message

Substituting [arsimp.shx] for [Swis721 Lt BT]

Substituting [arsimp.shx] for [Stylus BT]

when i trying to open a drawing prevously done in Acad 2007 and the font Swis721 LtBT, gets replace by some other font  how can i get  the drawing to open  as is i,e with the font Swis721 LtBT in draft sight. i have observed that the draftsight does not contain the font Swis721 LtBT & Stylus BT how to add it to draft sight?