When you sign a contract, do you need to have an "original" - i.e., one contract with the original signatures of all the parties - for it to be valid or enforceable?
When I first started practicing law in 1991 (28 years ago when the Internet was a baby), signing contracts and closing deals was very formal. Most deals were closed in person, with all the parties and their attorneys gathered around a table. The parties would customarily sign four copies of each document, one for each party and each party's attorney (if there were more than two parties, we would sign enough originals for each party and its attorney to have an original). Even if we did not conduct the closing in person, the parties would still sign four "originals," and the attorneys would see that each party and its attorney received the appropriate amount of fully signed originals, either by hand delivery, overnight delivery, or US Mail.
Over the years closings have become less formal as electronic communication has become easier and widespread. Almost all my closings are now done remotely; rarely do we have a closing where all parties are present in person. In addition, in most of those closings, the parties and their attorneys do not exchange originals. Instead, they exchange signed copies by email.
You might be concerned that if a dispute arises (e.g., breach of contract, collection matter, etc.), you won't be able to enforce a contract without an original signature. Fortunately, the law acknowledges that people might not ever receive, might not keep keep, or might misplace or lose an original. The enforceability of a contract should not hinge on the technicality of having an original. Therefore, the rules of evidence allow a party to submit a copy of a signed contract to a court as evidence of the existence of the contract. You can check your particular state's rules of evidence for the exact requirements for getting a copy admitted into evidence in lieu of the original.
In addition, you might consider how you draft or revise contracts and other legal documents in the future. For example, my practice is to include two provisions into a contract or other legal document to require the parties to expressly acknowledge that (1) they don't have to sign the same copy of the document for it to be enforceable - i.e., they each can sign a separate copy (called a "counterpart") and the two separate copies taken together will constitute one document; and (2) a PDF, electronic, or other digital copy of the signed document will have the same enforceability as the original.
So, don't lose sleep if you have a copy, but don't have the original.