فَوَجَدَ بَعْضَهَا تَالِفًا
He found some of them damaged.
Here “wajada,” used to mean 'find to be', takes two objects: “baʿḍahā” is the first and “tālifan” the second. The pronoun -hā refers back to “al-awrāq.” The noun “baʿḍ” confines the discovery to a portion of the leaves; it does not report damage to every leaf.
Replacing it with “wajada al-awrāqa tālifatan” would assert a broader finding about the set. The partitive wording therefore plays a semantic as well as a syntactic role.