Hi Yeshwant,
I regret for the delay in getting back to you on this.
We consider that you are using the Syncfusion - Super ToolTip. Please refer the below code snippet to set the font of the ToolTip text through code.
[C#]
Syncfusion.Windows.Forms.Tools.ToolTipInfo toolTipInfothroughCode = new Syncfusion.Windows.Forms.Tools.ToolTipInfo();
toolTipInfothroughCode.Header.Font = new System.Drawing.Font("Calibri", 10F,System.Drawing.FontStyle.Bold, System.Drawing.GraphicsUnit.Point, ((byte)(0)));
toolTipInfothroughCode.Body.Font = new System.Drawing.Font("Tahoma", 8.25F, System.Drawing.FontStyle.Strikeout, System.Drawing.GraphicsUnit.Point, ((byte)(0)));
Please try this and let me know if this helps.
http://websamples.syncfusion.com/samples/Tools.Windows/F69133/main.htmThank you for your patience.
Regards,
Nanda