Search does NOT search inside PDFs on Publisher however it works on Author

Hello 😃

Aa the title states, when I search for a piece of text within a PDF on Publisher it does not show any results. However, the same search on Author does provide results. I have reindexed lucene indexes and I'm using AEM service package 6.5.12.0. 

I have the feeling; I'm missing to publish a setting?

Any help would be much appreciated. 

If you need more details, feel free to ask 🙂

Thank you indeed.