When original document is unavailable?

When the original document has been lost or destroyed, or cannot be produced in court, the offeror, upon proof of its execution or existence and the cause of its unavailability without bad faith on his or her part, may prove its contents by a copy, or by recital of its contents in some authentic document, or by the testimony of witnesses in the order stated. (Section 5 Rule 130).

When original document is in adverse party’s custody or control. – If the document is in the custody or under the control of the adverse party, he or she must have reasonable notice to produce it. If after such notice and after satisfactory proof of its existence, he or she fails to produce the document, secondary evidence may be presented as in the case of its loss. (Section 6, Rule 139).

It is called the “Secondary Evidence” because the best evidence cannot be presented in court as it was lost or destroyed; or it is in custody or under the control of the opponent party; or the document is in the custody of public officer or is recorded in a public office.

Secondary evidence of the contents of a written instrument or document refers to evidence other than the original instrument or document itself. A party may present secondary evidence of the contents of a writing not only when the original is lost or destroyed, but also when it is in the custody or under the control of the adverse party (EDSA Shangri-La Hotel and Resort, Inc. vs. BF Corporation, 556 SCRA 25).

The conditions sine qua non for the presentation and reception of the photocopies of the original document as secondary evidence are: (a) There is proof of the original document’s execution or existence; (b) There is proof of the cause of the original document’s unavailability; and (c) The offeror is in good faith (Id).

A secondary evidence is admissible only upon compliance with Rule 130, Section 5, which states that: when the original has been lost or destroyed, or cannot be produced in court, the offeror, upon proof of its execution or existence and the cause of its unavailability without bad faith on his part, may prove its contents by a copy, or by a recital of its contents in some authentic document, or by the testimony of witnesses in the order stated. Accordingly, the offeror of the secondary evidence is burdened to satisfactorily prove the predicates thereof, namely: 

1. the execution or existence of the original;

2. the loss and destruction of the original or its non-production in court; and

3. the unavailability of the original is not due to bad faith on the part of the proponent/offeror. Proof of the due execution of the document and its subsequent loss would constitute the basis for the introduction of secondary evidence. (Santos v. Court of Appeals, 420 Phil. 110, 120 (2001).

Secondary evidence is evidence that has been reproduced from an original document or substituted for an original item. For example, a photocopy of a document or photograph would be considered secondary evidence. Another example would be an exact replica of an engine part that was contained in a motor vehicle. If the engine part is not the very same engine part that was inside the motor vehicle involved in the case, it is considered secondary evidence.
Courts prefer original, or primary, evidence. They try to avoid using secondary evidence wherever possible. This approach is called the best evidence rule. Nevertheless, a court may allow a party to introduce secondary evidence in a number of situations

(https://www.legalservicesindia.com/article/1334/Secondary-Evidence.html)