chore: add the PDF version to the learning materials (#2379)
chore: add the PDF version to the learning materials (#2379)


hltj/kotlin-web-site-cn,hltj/kotlin-web-site-cn,hltj/kotlin-web-site-cn,JetBrains/kotlin-web-site,hltj/kotlin-web-site-cn,hltj/kotlin-web-site-cn,JetBrains/kotlin-web-site,JetBrains/kotlin-web-site,hltj/kotlin-web-site-cn,JetBrains/kotlin-web-site,JetBrains/kotlin-web-site,JetBrains/kotlin-web-site