Short answer. Yes. Falsification is not limited to public officials. The Revised Penal Code punishes any private individual who falsifies a public, official or commercial document, and any person who falsifies a private document to the damage of another. Using a falsified document knowingly is punished as well.
What the law says
Any private individual who shall commit any of the falsifications enumerated in the next preceding article in any public or official document or letter of exchange or any other kind of commercial document
Revised Penal Code, Article 172 — Falsification By A Private Individual. Read the full provision →
What the law says
Any person who, to the damage of a third party, or with the intent to cause such damage, shall in any private document commit any of the acts of falsification enumerated in the next preceding article
Revised Penal Code, Article 172 — Falsification By A Private Individual. Read the full provision →
Read the current version, not the 1930 one
Before anything else, a warning about sources. The penalties and fines in this part of the Revised Penal Code were rewritten by Republic Act No. 10951 (2017), which raised property values and fine amounts throughout the Code. The fine for falsification by a private individual now runs up to one million pesos, alongside imprisonment in the form of prisión correccional in its medium and maximum periods. Many free reproductions of the Code still circulate the 1930 figures, which are far lower and no longer the law. If you are reading a penalty amount anywhere — a blog, an old textbook, a printed copy — check whether that source has been updated for RA 10951 before you rely on the number.
The kind of document changes what has to be proved
The law splits the offence in two. Where the falsified document is a public, official or commercial document — a deed, a birth record, a government form, a letter of exchange, a receipt or invoice used in trade — the offence is complete once the falsification is committed. Nobody has to show that a particular person lost money, because the harm the law protects against is the loss of public confidence in documents that everyone must be able to trust. Where the document is a private one, such as a letter, an internal record or an unnotarised agreement between two people, the prosecution must additionally show damage to a third party, or at least the intent to cause it.
Using a false document is its own offence
You do not have to be the forger to be charged. The article separately punishes anyone who knowingly introduces a false document in evidence in a judicial proceeding, and anyone who uses such a document to the damage of another or with intent to cause damage. That is punished by the penalty next lower in degree. The word doing the work is "knowingly" — a person who submits a document not realising it has been tampered with is in a different position from one who submits it aware of the defect. This is why people who merely passed along a document they received from someone else are sometimes swept into a complaint, and why what you knew and when becomes the central question.
What the provision does not cover
Not every untruth in writing is falsification. The acts punished are the specific ones the Code enumerates — counterfeiting a signature or handwriting, making it appear that persons took part in an act when they did not, attributing statements to people that they never made, altering true dates, changing the meaning of a genuine document, and similar acts. A statement that is merely inaccurate, an opinion someone disagrees with, or a document signed by a person who later regrets it does not become criminal for that reason. Falsification also frequently appears in combination with other offences when the false document is the means used to obtain money, and the interaction between the two changes the penalty. Anyone facing or considering such a complaint should have the actual document examined by counsel before filing or answering.