Shimon has in his vault a valuable document. Reuven knows everything there is on this document, but he wants a copy of it anyway. He's only going to use it for personal use, not to sell it. Being the nice guy he is, Reuven asks Shimon for permission to see this document. But he photocopies it while he has it, say for future reference. Now, when he returns it, he mentions to Shimon, "By the way, I hope you don't mind that I made a copy of your document."
Shimon is understandably annoyed by this act, but he's not sure there's anything he can do. Did Reuven violate lo signov? No. He had the document legally. Is there geneivas da'as? No. Shimon gave it to him willingly.
So: is there an issue with copying someone else's objects, assuming that there's no geneivas da'as or actual geneivah? What about in a case where Reuven decided to copy it only after he had it in his possession? Is that a Sholeiach Yad issue?