3 sentences

1. 随函附上证明，请台端查收。

   suí hán fù​shàng zhèng​míng, qǐng tái​duān chá​shōu.

   Enclosed is the certificate for your review.

   Source: Dong Chinese Dictionary

2. 我收到了学校的录取通知函。

   wǒ shōu​dào le xué​xiào de lù​qǔ tōng​zhī hán.

   I received the admission letter from the school.

   Source: Dong Chinese Dictionary

3. 这套线装书共有四函。

   zhè tào xiàn​zhuāng​shū gòng yǒu sì hán.

   This set of thread-bound books consists of four cases.

   Source: Dong Chinese Dictionary