Hello Samana Johann,
if pages are added externally, they are not directly in the search index, which means that the contents are not known by the wiki, what happened in your case. While using the wiki, the missing search index will be generated, but this will take some time. Further information to the search index can be found here:
https://www.dokuwiki.org/faq:searchindex
To (re-)generate the whole index instantly, you can use the searchindex-plugin:
https://www.dokuwiki.org/plugin:searchindex
Greetings,
Christoph