honeybear.ai is an AI-based PDF reader good for big PDFs (up to 400 pages) and scanned documents. It's got features like notes, image export and text summarization that can be useful for people wrestling with dense documents like research papers and academic papers.
Another good option is PDFgear, which offers a range of tools to read, edit, convert, merge, sign and annotate PDF files for free with no registration required. It's got OCR for extracting text from image-based documents and works on Windows, macOS, Android and iOS, making it useful for personal and professional use.
If you want to use natural language to interact with PDFs, ChatPDF is worth a look. This AI-based system lets you upload hundreds of PDFs, ask questions about them and generate text summaries. With strong data security and support for more than 95 languages, it's good for students, researchers and customer support agents.