"Auto-fill" means different things depending on the tool. Adobe Acrobat's Auto-Complete remembers values you've typed before and suggests them in similar fields later — useful, but it only works on PDFs that already have interactive form fields, and it only recalls what you've personally typed on that device before. An AI-based filler works differently: it reads the form itself, figures out what each field is asking for, and fills it from information you've already saved — including on scanned or flat PDFs that have no interactive fields at all.
To auto-fill a PDF form online, upload it to an AI form filler that detects each field (using OCR if the PDF is scanned), then fills it from your saved details or a client profile — review the AI-filled values, adjust anything flagged, and export or e-sign. This works without installing Adobe Acrobat or any desktop software, directly in a browser.
What's the difference between Acrobat's Auto-Complete and an AI form filler?
Auto-Complete is a browser-style autofill: it remembers text you've typed into similar fields before and offers it as a suggestion, field by field, only within Acrobat and only on PDFs with real form fields. An AI form filler instead reads the whole document, identifies what information each field needs (name, date, address, signature) even if the PDF was scanned from paper, and fills the entire form in one pass from information you provide once — closer to filling out the form for you than to autocomplete's memory-based suggestions.
Can I auto-fill a scanned PDF that has no fillable fields?
Yes, if the tool includes OCR (optical character recognition). OCR reads the text and layout of a scanned image and reconstructs where each field belongs, so the form can be filled even though it started as a flat picture of a page rather than an interactive PDF. This matters for older government forms, faxed documents, or anything scanned from a paper original — Acrobat's own Auto-Complete can't touch these at all.
What are the actual steps to auto-fill a PDF online?
Upload the PDF (or Word file) to a form filler like Filly. The AI scans it and detects every field, whether the PDF has built-in form fields or is a flat scan. Enter your details once, or select a saved client profile if you're filling the same information you've used before. Review the filled values — each one is typically flagged by how confident the AI is, so you can quickly spot-check anything uncertain rather than re-reading the whole document. Then export the completed PDF or send it for e-signature.
Do I need to re-enter my details every time I fill a new form?
Not if you save them as a reusable profile. Your name, address, and other repeated details carry over automatically to the next form, whether it's the same document again or a completely different one that happens to ask for the same information — see filling any PDF form online for free for the general workflow this builds on.
What should I double-check after an AI fills a form automatically?
Review every field flagged as low-confidence before exporting — these are usually places where the source text was ambiguous (handwriting on a scan, a field that could plausibly hold two different values) rather than the AI failing outright. Names, dates, and ID numbers are worth a manual glance even on high-confidence fields, since a single wrong digit on something like a tax ID or date of birth can cause real problems downstream.
Which tool should I use if I'm comparing options?
It depends on what you're filling most: dense multi-page PDFs, forms that need to go out for signature, or the same form repeated for many people all favor different feature sets. See a comparison of tools for auto-filling PDF forms for how the major options differ on OCR, batch filling, and e-signature.
Frequently asked questions
Is auto-filling a PDF form with Filly free?
Yes, up to the free plan's limit of 10 filled documents a month, no credit card required.
Does auto-fill work on Word documents too, or only PDFs?
Both — Word forms can be uploaded and auto-filled the same way as PDFs.
What if the AI fills a field incorrectly?
Edit any field directly before exporting — the AI's fill is a starting point you review and correct, not a final, unchangeable output.
Can I auto-fill the same form for multiple people at once?
Yes, using batch fill (a paid-plan feature), which applies one form across several saved profiles in a single run instead of filling each copy individually.