We interact with PDF files so often now, it's almost easy to forget how ubiquitous they've become. It's no wonder then that different developers keep making apps that address specific needs to work with a PDF file, even when there are already so many great online PDF editors. From searching multiple PDF files together to using a ChatGPT AI to read and answer questions about it, there's an app for everything.

1. ChatPDF (Web): Upload PDF Files and Get Answers From ChatGPT

ChatPDF uses ChatGPT to read your PDF file, after which you can ask questions and get answers like a chatbot

When you have a PDF file with a lot of pages, it can be difficult to find the relevant information from a simple Ctrl+F search. ChatPDF offers a better option where you upload the file to their website, where ChatGPT will read the PDF and then answer questions that you ask.

It works shockingly well, scanning your entire PDF to give you ChatGPT-like answers that condense information from multiple paragraphs. In our test, images and data from tables weren't recognized by ChatPDF, but it had a good understanding of all textual material. You can upload PDFs from your hard drive or a linked URL.

ChatPDF currently uses ChatGPT 3.5, and is looking into how to incorporate the newer ChatGPT 4. The free version analyzes a maximum of three PDF files per day, with up to 120 pages in each file, of which you can ask 50 questions a day. ChatPDF Plus ($5 per month) allows 2000 pages per PDF for 50 PDFs a day, and you can ask 1000 questions daily.

2. Human Eyes Only (Web): Make PDF Files Unreadable by Software and Bots

Human Eyes Only disables OCR on your PDF files so that software, bots, and AI can't read it

Like ChatPDF, there's an influx of other apps that use AI to read and analyze PDFs. And for the longest time, there have been other software where the machine is "reading" your PDF, like ATS scanners for resumes. While this technology has several benefits, it can easily be used against you if someone with bad intentions gets hold of a set of PDFs that contain sensitive information. And that's where Human Eyes Only (HEO) comes in.

In a nutshell, the web app renders your PDF in such a way that it's unreadable for bots. To a human eye, it still looks like regular English. But HEO plays around with the base fonts that a machine recognizes in a PDF, making simple English look like gibberish characters that you'd find in a font like Wingdings.

There are several uses for this. You make documents immune to AI and bots in a jiffy. And even if a human tries to copy-paste content from a PDF to a text file, they'll only get gibberish in the text, making it difficult to steal intellectual property. To put it simply, HEO nullifies optical character recognition (OCR) for computers, thus protecting PDF files from technological tricks.

3. Desklamp (Web): Add Notes, Highlights, and Collaborate on PDFs

Often, textbooks, reference materials, and books are now in a PDF format. So you need tools to highlight important bits, write notes, save and bookmark parts for later, and share these with friends if necessary. Desklamp is a fantastic app for students looking to collaborate and annotate on PDF files.

For any PDF file that you upload, Desklamp adds a pane on the right for your personal space. There are three basic parts in that. The first is Notebook, where you add detailed notes, and link them to the relevant sections of the page. If you copy-paste excerpts, Desklamp automatically links them to the PDF.

In Annotations, you will use highlights (which you can color-code), underlines, and sticky notes. And in Clipboard, you can save images and markers from the PDF file so you don't have to go back-and-forth each time. You can arrange all these notes, annotations, and clips with tags to find them later easily.

Desklamp also has an interesting collaboration feature, where you can invite friends to work on the same PDF. It's a bit like sharing your notes for a textbook in the physical world. And you can back up everything to the cloud so you don't lose your data.

4. PDFGrep (Web): Search Contents of Multiple PDF Files at Once

PDFGrep lets you upload multiple PDF files and search all of them at the same time

Sometimes, it's the tiny little tools that make the biggest impact. PDFGrep checks all the boxes: it solves a pressing need and executes it perfectly, it's completely free with unlimited use, and it respects your privacy.

The web app's core feature is to let you search across multiple PDF files. Upload as many files as you want, and use the search box for your terms. You'll then get a list of all the places where you can find the keyword in the files, and clicking any will take you to that part. It's actually a handy tool to use even on a single file as it's better than the view you get with Ctrl+F in any PDF reader.

PDFGrep is completely local, so your files are never uploaded to any server, thus protecting your privacy. That's what also makes the app lightning-quick, since all the processing is happening on your browser. And as a bonus, the built-in PDF reader is actually quite good.

5. PDF Shelter (Web): Suite of No-Cloud PDF Editing Tools

PDF Shelter has a series of PDF editing tools (merge, split, delete pages, convert to JPG) that work within your browser without uploading to servers

Most online PDF editing suites, like the popular and fantastic ILovePDF, operate by uploading your files to cloud servers, processing them remotely, and then making them available as downloads. This raises privacy and security concerns when you're dealing with sensitive files, and can make the processing a lot longer if you're dealing with large files. That's why we're increasingly seeing more online PDF editors that run locally on your browser, giving you faster speeds, and better security and privacy.

PDF Shelter is the latest in this line of locally processing online PDF tools. It currently lets you convert JPGs to PDFs and back, merge or split PDFs, and delete pages in a file. It's completely free with no restrictions. You don't need to register or sign up to use it.

6. PDF Decryptor (Web): Free App to Make Passwordless Copies of Protected PDFs

PDF Decryptor can create password-less copies of password-protected PDFs for free

Let's say you have a password-protected PDF file, whose password you know. If you try to make a copy of it that doesn't require a password, you'll find that all apps to do that are the paid PDF editors. PDF Decryptor solves that in the form of an online app that creates password-free copies of protected PDFs for free.

Please note that PDF Decryptor won't work if you don't know the password of the original file. You can't use this to remove passwords from protected PDF files.

When to Pay for PDF Editors

With so many free online apps to work with PDF files, you might be wondering why you would ever need to pay for PDF editor apps. At this point, for a regular user, you really can get by with the free options online. However, if you use PDFs almost daily for work purposes, investing in a desktop PDF editor app like Adobe Acrobat could pay off as it'll be faster and protect your privacy and security.