This is the 493rd most frequent Arabic word.
بمناسبة
On the occasion of.
Here, 'بمناسبة' is used to indicate that the reason for congratulating is the occasion of a birthday.
أُهنئك بمناسبة عيد ميلادك.
I congratulate you on your birthday.
In this sentence, 'بمناسبة' expresses the reason or occasion related to the action of distributing flowers.
تم توزيع الزهور بمناسبة افتتاح المعرض.
Flowers were distributed on the occasion of the exhibition opening.
This usage of 'بمناسبة' highlights the purpose or occasion of the gathering, marking the company's anniversary.