Conversion is a tort that exposes you to liability for damages in a civil lawsuit. It applies when someone intentionally interferes with personal property belonging to another person. To make out a conversion claim, a plaintiff must establish four elements:
The most direct and obvious way to commit conversion is by taking personal property that belongs to someone else without permission. For example, if you take a framed photograph from the wall of a local restaurant or a document from someone's desk, you may be held liable for conversion, assuming you retain the property for a substantial period of time and thereby interfere with the rightful owner's use and possession of it. It does not matter whether you intend to publish the information, photos, or other content.
However, if you remove paperwork or photographs from someone's office or home temporarily in order to copy the information -- intending to return the documents to the owner -- you might not be liable for conversion because this temporary interference does not necessarily deprive the rightful owner of the possession or use of the property. See Harper & Row Pubs. v. Nation Enters., 723 F.2d 195, 201 (2nd Cir. 1983) ("Conversion requires not merely temporary interference with property rights, but the exercise of unauthorized dominion and control to the complete exclusion of the rightful possessor."). You should be aware that taking property from someone can also expose you to criminal liability under state laws.
You can also commit conversion by receiving and retaining property from someone who does not have the right to give the property away. This issue could come up when you receive documents from sources. For example, if a bank employee gives you checking account records for bank customers, you may both be liable for conversion because the employee likely does not have permission from his or her employer to turn over a customer's records. But the legal analysis is not that simple, and whether or not you could be held liable for conversion under these circumstances depends on whether the records you receive are originals or copies.
As a rule of thumb, you can generally receive and retain copies of documents that belong to someone else, but you may not receive and retain the originals of such documents. The reason is that "the possession of copies of documents -- as opposed to the documents themselves -- does not amount to an interference with the owner's property sufficient to constitute conversion." FMC Corp. v. Capital Cities/ABC, Inc., 915 F.2d 300, 303 (7th Cir. 1990). However, you may be held liable for conversion for receiving and retaining copies if the rightful owner no longer has either originals or copies of the documents in question. Even if you are held liable for conversion and must return the documents in question, you generally are entitled under the First Amendment to retain copies of the documents for yourself and to disseminate any information contained in them. See id. at 304-05.
If you receive classified documents or other information relating to national security from a government employee, you may subject yourself to criminal liability under federal espionage-related laws. See the section on Receiving Documents and Information from Government Sources for details.