An altered document is a questioned document that has been changed for the purpose of deceiving someone. This may be where a person used the same color pen to change a smaller number to a larger number. An example is changing a 1 to a 4 or 7. Another example is removal of part of a document and placing new text in place of the removed text. An example is removing the handwritten portion of a check and writing in new information such as a pay to name.

An electronically created document such as a word processor document can be altered. An example is changing the text in a document. A person may change the terms of a contract by using a computer.

Tools such alternate light sources such as infrared and ultraviolet are used to discover an altered document. Adobe Photoshop is also used to discover an altered document after it has been scanned into the computer.