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Most Document Security Papers incorporate "Hidden Message Technology." There are a number of patented methods used to accomplish this task. However due to changing copier technology, you may find that your document can be duplicated on some photo copiers without the words "VOID" "COPY" or other hidden messages showing up on the copy. For this reason we advise purchasing document security paper that incorporates more than one security feature.
Remember, the reason document security paper is used is to "prevent accurate document duplication." A document printed on Security Paper that contains numerous security features, features such as "color change ink" for example, is virtually impossible to accurately duplicate using a standard or color copier, scanner or even a digital camera.
Security Paper is used to help prevent the unauthorized duplication of any document.
To secure a document, it is very important to use multiple security features.
A document that contains only one feature, a VOID background for example, may be duplicated on some photo copiers without the word VOID showing up on the copy.

The reason the United States Government does not include hidden message technology in US currency is because it does not work 100% of the time.