The procedural requirements in filing original actions before the Court of
Appeals is provided in Section 3, Rule 46 of the Rules of Court, to wit:
SEC. 3. Contents and filing of petition; effect of non-compliance with
requirements. - The petition shall contain the full names and actual addresses
of all the petitioners and respondents, a concise statement of the matters
involved, the factual background of the case, and the grounds relied upon for
the relief prayed for.
In actions filed under Rule 65, the petition
shall further indicate the material dates showing when notice of the judgment
or final order or resolution subject thereof was received, when a motion for
new trial or reconsideration, if any, was filed and when notice of the denial
thereof was received.
It shall be filed in seven (7) clearly
legible copies together with proof of service thereof on the respondent with the original copy intended for the court indicated as such by the
petitioner, and shall be accompanied by clearly legible duplicate original or
certified true copy of the judgment, order, resolution, or ruling subject
thereof, such material portions of the record as are referred to therein, and
other documents relevant or pertinent thereto x x x
x x x x
The
failure of the petitioner to comply
with any of the foregoing requirements shall be
sufficient ground for the dismissal of the petition. (Emphasis and underscoring supplied)

Admittedly, the Rules require that the petition filed before the CA should
include proof of service to the other party. Essentially, the purpose of this rule is to apprise such party of the
pendency of an action in the CA. Thus, if such party had already been notified
of the same and had even participated in the proceedings, such purpose would
have already been served.