Best AI app for documents in 2026: 7 apps ranked on filled PDFs and the file you get back

Which AI app is best for documents? Whizi's website, when you need your own file back

Our test: does the app return your own file edited (or at least a new file), how many of Claude, GPT and Gemini read it on one plan, and, to break ties, how big a file it takes? Whizi is the one app here that passes both of the first two steps. It returns your own PDF edited, on its website only, and its $29.99 Pro plan reaches all three families. None of the OpenAI, Anthropic or Google help pages we read on 21 October 2026 mentions filling a form you attached.

A size cap tells you what an app accepts, not how much the model reads. Claude takes a 500 MB upload in a chat, yet its file tool, the part that builds and edits files, caps each file at 30 MB in and out. Gemini's free plan holds a 32K token window, about 48 pages by Google's own ratio of 1,500 pages per million tokens. Whizi reads about the first 130,000 characters of an Office file each turn on most models, and it warns you when a file runs longer. Big files and long files aren't the same problem.

How do 7 AI apps handle a PDF, Word file or spreadsheet?

We built this table from each vendor's help pages and, for Whizi, from its own code, all as of October 2026. "Edits your own file" means the original file changes, not a new copy built from its text:

Two columns decide most picks. If your document lives in Excel or Word all day, an assistant that edits the open file beats any chat app. Claude and ChatGPT have add-ins, and Copilot is built into Microsoft 365. If the document is a PDF someone sent you, the add-ins don't help. That's where a filled or edited copy of the original PDF matters, and Whizi's website is built for it.

Which AI app is best for document editing? It depends where the file lives

Whizi is best for PDFs you need back filled or edited, ChatGPT for big files and Google Docs, and Claude for Excel, Word and PowerPoint. We took every pick from the vendor's own help page or App Store listing, and gave every app a losing case from the same sources:

ChatGPT and Claude tie on the first two steps. Each edits your own files, and each reads them with one model family. The tiebreak gives second place to ChatGPT, which takes a 512 MB file against Claude's 500 MB in a chat. OpenAI's ChatGPT Work help page says it "can create or edit documents, spreadsheets, presentations, reports, and analyses." Claude's strengths sit in its Best for line. It makes real files even on Free, and Anthropic's Claude for Excel page promises it will "adjust assumptions while keeping formula relationships intact."

Gemini and Copilot tie the same way. Gemini works inside Docs and Sheets on Google AI Pro, $19.99 a month in the iPhone app, and Copilot inside Word, Excel and PowerPoint on Microsoft 365. Gemini takes a 100 MB file to Copilot's 50 MB, so it ranks fourth. The Gemini app is another matter. Its export help page says Export to Docs "saves a new doc in Google Drive." Perplexity beats Grok a step earlier. One Perplexity Pro plan lets you pick GPT, Claude Sonnet or Gemini Pro, while Grok reads with Grok alone.

Not every document tool is a chat app. Adobe's Acrobat Studio costs $24.99 a month on an annual plan, and Adobe says its AI Assistant can "edit, sign, redact, and compress your docs." It works on PDFs only. You'd keep a chat app for Word and Excel. We left PDF chat sites such as ChatPDF and ChatDOC out on purpose. This list covers chat apps you'd use for every kind of document, and a PDF chat site is a single tool you'd add next to one, like Acrobat.

Whizi, which publishes this page, is the newest app on the list and loses on trust. It went live on the App Store on 26 August 2026 and had 3 US ratings on 11 October, against 11,187,768 for ChatGPT. There's no iPad version, and it has no widget or Siri action. Form filling and PDF edits run on the website only, and files in the iPhone and Android apps are capped at 10 MB each. A Word or Excel file you ask it to change comes back as a new .docx or .xlsx built from the content, so the original styling isn't kept. The free tier is thin: text only, on Whizi AI and Auto. What it does differently is send the original PDF file, not text pulled from it, to Claude, GPT or Gemini on paid plans (up to 6 PDFs, 12 MB and 100 pages a turn). Its catalog holds 280+ models. Perplexity Pro reaches those three families too, but it cuts long files to their most important parts. For more apps that bundle several model families, see our all in one AI platforms comparison.

Which AI app can fill out a PDF form? Whizi's website does it on the original page

Whizi's website fills the PDF form you attach and gives you back the same file. It finds the form's boxes when you attach it: real form fields, boxes drawn as lines, and boxes on a scan or a phone photo. You tell the model what goes where in plain words. The browser then writes those values into the original pages with logos, barcodes and layout untouched. A photo of a paper form comes back as the same photo, filled in.

Editing works the same way for text you want changed. Ask Whizi on the website to swap a tenant's name, a rent amount or a date in a contract PDF, and it changes those words on the original pages. If you add or remove whole clauses, it builds a new document instead, since the old pages can't hold them.

The big three describe other routes. Anthropic's file creation page, updated 6 August 2026, lists .xlsx, .pptx, .docx and PDF output for all Claude users, Free included. It doesn't mention filling a form you uploaded. OpenAI's ChatGPT Work page tells you to say what must stay unchanged, such as "formulas, layout, tone, branding." That's good advice for any of these apps. Check the result before you sign it.

What is the best free AI app for documents?

Claude has the most useful free plan for documents, because it makes real files on Free. Anthropic's help center says file creation "is available to all Claude users (Free, Pro, Max, Team, and Enterprise)." It counts against your usage limits faster than plain chat does.

ChatGPT Free reads big files but few of them. OpenAI's File Uploads FAQ allows 512 MB per file on every plan and 3 uploads a day on Free. Gemini's free plan takes 10 files a prompt at up to 100 MB each, but its 32K window reads about 48 pages. Microsoft's free Copilot app takes 20 files a chat at 50 MB each. Whizi's free tier gives 7 messages on day one and 3 a day after, so it won't carry real document work.