You were given a specific Pantone color (e.g. PANTONE 301C) to use for an AutoCAD drawing object and you want to set this specific color (or its RGB equivalent) in AutoCAD.
Since AutoCAD 2004 you can directly use named colors from the Pantone and RAL color palettes.
Start the COLOR command or click the "Select color" item in the Color control of the Properties palette, Quick Properties palette or in the control bar or ribbon. In the Select color dialog, go to the "Color books" tab (the 3rd).
A typical Pantone color is defined by a name ending with "C" (coated) or "U" (uncoated) or "M" (matte). These colors are contained in the respective Pantone color books "PANTONE(R) solid coated", "PANTONE(R) solid uncoated" and "PANTONE(R) solid matte". So the above mentioned example - PANTONE 301C - can be found in the "PANTONE(R) solid coated" color book. Select this color book and just type in or copy-paste the color name in the "Color" textbox. You can use either "PANTONE 301C" or "PANTONE 301 C" or e.g. "PaNtOnE -- 301c" - AutoCAD will recognize the right color. At the same time you can see its RGB components (estimated, there are no direct equivalents) in the color dialog.
Select Pantone color in AutoCAD 2009 CZ