First up is ChatPDF, which is really good at understanding PDFs, especially research papers, academic papers and legal contracts. You can upload a PDF and ask questions and it'll respond with answers and a summary. It can handle multi-file chats and PDFs in any language, so it's pretty flexible.
Another good option is Notedly, which is geared for students and others who want to quickly understand complex information in textbooks, news articles, lectures and PDFs. It offers auto summarization, simplification of complex content and PDF summarization, all designed to free up time and reduce reading anxiety.