Before you fill in a single field, work out which of the three kinds of PDF form you are holding. It determines everything about how the job goes, and it explains why the last form you filled in was effortless and this one is fighting you.
The three kinds of PDF form
Interactive forms have real fields built into the file. Click and a cursor appears; press Tab and it jumps to the next box. The document contains proper form objects — an AcroForm, in the specification's language — with names, types, and validation rules. These are the pleasant ones. Any PDF reader can fill them, including your browser, and the data is stored as structured values rather than drawn text.
Flat forms look like forms but contain no fields at all. They are a page with lines and boxes printed on it. Clicking does nothing because there is nothing to click. This happens when a form was designed in Word or InDesign and exported straight to PDF without adding interactive fields. Most forms you download from small organisations are like this.
Scanned forms are photographs of paper. No fields, no selectable text, just an image. Anything printed, filled in by hand, or run through a scanner ends up here.
To tell them apart in two seconds: click in a field. Cursor and highlight means interactive. Nothing means flat or scanned. Then try to select the printed text with your mouse — if you can, it is flat; if you cannot, it is scanned.
Filling an interactive form
You may not need a tool at all. Open the PDF in Chrome, Edge, Firefox, or Preview on a Mac, click into the fields, type, and save. All of them handle interactive forms and save your entries.
Things to know:
- Tab moves between fields in the order the designer set, which is occasionally nonsensical. If Tab jumps somewhere unexpected, click directly instead.
- Save, do not print-to-PDF, if the recipient needs the data. Printing flattens the values into the page and discards the structured field data some organisations extract automatically.
- Dropdowns and radio buttons only accept their predefined options. If none of them fits your situation, that is a flaw in the form, and the right move is to ask rather than to force it.
- Field text can overflow invisibly. A long address may be truncated on screen or on print. Check the rendered result rather than trusting the input box.
- Flatten before sending if you do not want the recipient editing your answers. See how to flatten a PDF.
Filling a flat or scanned form
Here you are not filling fields — you are drawing text on top of a page. This is what a browser editor like Docento.app is for, and it works identically on flat and scanned documents, because in both cases you are overlaying rather than typing into anything.
- Open the form. Drag the PDF into the editor. It is read by your own machine, which matters when the form asks for your national insurance number, bank details, or medical history.
- Place text. Select the text tool and click where the answer belongs. Type. Adjust size so it sits comfortably within the line rather than crowding it.
- Tick the boxes. The stamp tool places a checkmark or cross. Click inside each box. Zoom in first — a tick straddling two checkboxes creates real ambiguity on a form that matters.
- Sign it. Use the signature tool to draw, type, or upload your signature, then place and size it on the signature line. Signing a PDF covers this in more depth.
- Date it. Almost every form has a date field and it is the most commonly forgotten one.
- Export, then open the result and read it as if you were the recipient.
Getting it to look right
Match the size of the printed text. Answers noticeably larger or smaller than the form's own labels look wrong. Most forms sit around 10–12pt; start there.
Use the arrow keys. Dragging with a mouse gets you close; nudging with arrow keys gets you aligned. Text that floats above the line is the single most common giveaway of a hastily completed form.
Sit on the line, not above it. Baselines are subtle. Zoom to 150% or more when positioning anything that has to align with a printed rule.
Keep colour consistent. Black for everything, unless the form asks otherwise. Dark blue is conventional for signatures on some documents and out of place on others.
Do not fight a broken form. If a field is far too small for the answer, write "see attached" and attach a page rather than shrinking your text to six points.
Common problems
The form will not open in the editor. Many official forms are encrypted or permission-restricted. If it opens in a reader but not an editor, print it to a new PDF using your system's "Save as PDF" option and work on that copy.
It is an XFA form. Some government and financial institutions issue forms built on XFA, an Adobe-specific technology that most tools — including browsers — cannot render. You will usually see a message asking you to open the file in Adobe Acrobat Reader. That message is accurate: use Acrobat Reader, which is free. See XFA forms explained.
Your entries vanished after saving. Some readers historically allowed filling but not saving of field data. Modern browsers and readers save fine; if yours does not, fill it, then print to PDF to preserve the visible result.
The finished file is too large to email. Scanned forms are image-heavy and often exceed attachment limits once completed. Compressing it usually solves this without hurting legibility.
It came back rejected as illegible. Almost always a scan issue rather than a filling issue — see scanning documents with your phone for how to get a clean capture.
A last check before you send
Read the completed form once, slowly, against the original questions. Confirm every required field is populated, the date is present, the signature is on the right line, and nothing you typed sits over the top of printed text. Then save your own copy under a name you will recognise later. Forms have a way of needing to be produced again months after you have forgotten they existed.
