Have an iPad 5th generation, IOS 12. iBook odd issues highlighting PDF files with Markup. Any alternatives?

Have an iPad 5th generation. I have issues with Pdf files in iBook when highlighting. The app uses Markup, which is fine, but there are odd issues. 1. Highlighting sizes are different from page to page. 2. Most pages highlighting is too small or too large. 3. Some pages are fine, but it’s rare. Any plans for Apple to adjust the size feature to allow “user defined size” for highlighting?

Any alternative free apps out there that have text to speech and highlighting? It would be best if Apple FIXED THIS, but us little people don’t make those changes. I can use the “You Doodle” app on my photos for edits, so I think Apple should incorporate a similar concept in iBooks as well. Or is that something “You Doodle” would have to incorporate in their app? Thank you!