Improve PDF parsing

[cbldev]

Is your feature request related to a problem? Please describe.
I noticed that on some complex PDF, with tables, the system pdftotext produce better result than pdf-reader gem.
I started this PR on an open-source project using langchainrb: https://github.com/nosia-ai/nosia/pull/20/files

Describe the solution you'd like
Maybe another option than pdf-reader here:

langchainrb/lib/langchain/processors/pdf.rb

Line 17 in 2054ef0

::PDF::Reader

Or an improvement in pdf-reader: https://github.com/yob/pdf-reader

Describe alternatives you've considered
pdftotext: https://www.xpdfreader.com/pdftotext-man.html