Some PDFs let you click into a box and type your name. Others look identical but go totally inert when you try. The difference is whether someone bothered to define form fields when the file was created.
What a form field actually is
A PDF form field is an invisible interactive region attached to a specific spot on the page. Text fields, checkboxes, radio buttons, dropdowns, and signature fields are all variations. Source apps like Word or Acrobat let designers draw these regions and configure validation (required, numbers only, date format). When you click into one, your viewer routes input there. Saving stores the entered data inside the file.
When there's no form to fill
Plenty of PDFs labelled 'application form' have no fillable fields — they were exported flat. To fill them anyway, open in Flint's editor and add text directly on top of the page. It looks identical to a real form field, just with no validation. Save, send, done. This is faster than asking the sender to redo the file.
Flattening before sending
Form data lives in a separate layer from the page until you flatten. Unflattened forms can be cleared by anyone who opens them, which is fine for collaborative drafts but bad for final submissions. Flattening bakes the entries into the page so they can't be cleared. Some tools do this automatically when you 'print to PDF'; in Flint, you can do it explicitly before sending the file off.
FAQ
Why won't my keyboard work on this form?
Either the field isn't a real field (just printed lines on the page), or the form was locked. For the first, type on top via an editor. For the second, ask the sender for an unlocked version.
Can I save a half-filled form?
Yes — most viewers save in-progress form data. Older viewers sometimes lose entries on save; if you've spent ten minutes on one, save a copy partway through to be safe.
Are fillable PDFs accessible?
Well-designed ones are — fields can carry labels and tab orders that screen readers follow. Many real-world forms skip this. If accessibility matters, prefer forms in HTML over PDFs.
If the field exists, click and type. If it doesn't, Flint adds text on top so you're not stuck reprinting and hand-writing.