The main passive-participle form for a basic triliteral is مَفْعُولٌ, with regular inflected variants where semantics and agreement allow them.
FormExampleSense
Masculine singularمَكْتُوبٌA written item
Masculine dualمَكْتُوبَانِTwo written items
Masculine sound pluralمَكْتُوبُونَWritten/registered male persons
Feminine singularمَكْتُوبَةٌOne feminine written item
Feminine sound pluralمَكْتُوبَاتٌWritten items (feminine form)
Choosing a plural also depends on whether the noun refers to people or nonhuman things and on established Arabic usage.