For inserting a data object as for example a mathematical formula or special characters like Greek characters into a text document, instruction symbols representing the data object are inputted in the form of text characters into the text document. A text portion containing instruction symbols is selected, and the instruction symbols contained in the selected text portion are converted into a data object represented by the instruction symbols. The invention allows rapid input of data objects into the text document, in particular simple mathematical formulae or single special characters without entering a formula editor or the like.