I have try that as well and the problem was still unsolved.
The rebuildSearchIndex was still not indexing the pdf files.
Since indexing pdf files is fundamental I spend some time debugging.
I believe there was a mistake in the code so I created a pull request and added a short explanation.
After the code I added the indexing for pdf files works.
Please let me know if there is actually an issue with the code or it is just my mistake.
Thank you for your help