Question: I need a simple and secure way to manipulate PDFs - is there a service that offers a conversational interface and pay-as-you-go pricing?

If you want a basic but secure way to manipulate PDFs with a conversational interface and pay-as-you-go pricing, pdfAssistant is a top contender. This AI chatbot lets you do a lot of PDF-related things, including converting, compressing, merging, adding watermarks or passwords, and more, all through a conversational interface. pdfAssistant employs industry-standard technologies for security and reliability and uses a pay-as-you-go credit system with no expiration dates, so it's a good way to get what you need out of your digital documents without breaking the bank.

Another top contender is HiPDF, an all-purpose PDF tool powered by AI. It includes chat with PDFs, document summarizing, reading, converting and editing, plus image tools and encryption for secure files. HiPDF supports multiple languages and comes with 10GB of free cloud storage, so it's good for personal and professional use.

If you need more advanced interaction and summarization abilities, ChatPDF could be just the ticket. This service uses large language GPT-4 technology to let you upload and interact with PDFs, generate text and ask natural language questions. It has different pricing tiers and protects your data with files stored in the EU under GDPR and encrypted while in transit. That could be useful for students, researchers or customer support agents who want to be more productive and make more informed decisions.