Word 2007 is a word processor program developed by Microsoft. One of the features of the program is the capability to insert thousands of different symbols and characters. Among those symbols is the reversible reaction arrow, composed of two arrows, positioned one atop the other, pointing in opposite directions. The symbol is used in chemistry to represent two reactants reacting together rather than one reacting on another. Open the document you wish to place a reversible reaction arrow in. Place your cursor in the document where you would like to insert the symbol. Click on the "Insert" tab, click on the "Symbol" button and select "More Symbols." Select "Wingdings 3" from the "Font" drop-down menu. Type "68" into the "Character Code" text box. This highlights the reversible reaction arrow symbol. Double-click the arrow to insert it into the document.