How to Fill Out a PDF Form: Fillable and Flat Forms Explained

How you fill out a PDF form depends on what kind of form it is. A fillable form has interactive fields, so you click into a box and type, tick checkboxes and pick from dropdowns. A flat form is just a picture of a form, so you need to place text boxes on top of the blank lines yourself. Once you know which one you have, filling it out takes a few minutes in a browser, in Preview on a Mac, in the free Adobe Reader, or in a private in-browser tool.

This guide explains how to identify each type, walks through filling both, and covers the save and send steps where most people lose their answers.

Fillable vs. flat forms

Fillable forms

A fillable PDF contains form fields defined inside the file. These are sometimes called AcroForm fields. Typical field types include:

• Text fields for names, dates and addresses.
• Checkboxes for yes or no answers.
• Radio buttons where only one option in a group can be chosen.
• Dropdowns and list boxes for picking from preset values.
• Signature fields reserved for digital signatures.

Fillable forms remember your entries in a structured way, which makes them easy to edit, and some organizations process them automatically.

Flat forms

A flat form has no fields at all. It may have been scanned from paper, or exported to PDF without the form layer. Clicking on a line does nothing. To fill it digitally, you add text on top of the page at the right positions.

XFA forms: the awkward third category

Some government and corporate forms use an older Adobe format called XFA. These dynamic forms often display a message like "Please wait..." or a notice to open the file in Adobe Reader when viewed in other software. Most browsers and third-party tools cannot fill them properly. If you see that message, the practical option is usually to open the form in Adobe Reader, which still supports XFA on desktop, or to ask the issuer for a standard PDF version.

How to tell which type you have

1. Open the PDF and click on a blank line. If a cursor appears inside a box, it is fillable.
2. Look for highlighted fields. Many viewers shade fields in light blue or show a banner saying the document contains fillable fields.
3. Try the Tab key. In a fillable form, Tab jumps from one field to the next.
4. Check whether the text is selectable. In a scanned flat form, the entire page is often one image. You cannot select the printed labels, and you will need to add text on top.

Filling a fillable form

In your web browser

Chrome, Edge, Firefox and Safari all include PDF viewers that can fill many standard fillable forms.

1. Open the PDF in the browser, either from a website or by dragging the file into a browser window.
2. Click each field and type, or tick the boxes.
3. Use the download or save button in the PDF toolbar to save a copy with your entries.

Browser viewers vary in how well they handle calculations, special formatting and scripts, so review the saved file afterward.

In Preview on a Mac

Preview detects form fields automatically. Click into a field to type, and choose File > Save or File > Export as PDF when you are done. If Preview does not show fields on a form you expected to be fillable, it may be an XFA form or a flat one.

In Adobe Reader

The free Adobe Reader fully supports fillable forms, including many with calculations and validation scripts. Open the form, type into fields, and save. Reader also offers Fill & Sign for adding text to flat forms.

In your browser with our form filler

Our free Fill PDF form tool finds the fields in your document and lets you complete them on any device. Processing happens locally, so personal information such as your address, date of birth or tax number never leaves your browser.

1. Open Fill PDF form and add the PDF.
2. Type into text fields, tick checkboxes, and choose options from dropdowns and lists.
3. Decide whether to flatten the result. Flattening turns your answers into regular page content so they cannot be edited later, which is a good choice for a final submission. Leave it off if you might need to update the form.
4. Download the completed PDF.

The tool also handles entries beyond basic English letters, such as Polish accented characters or Cyrillic text, by using a font that can display them.

Filling a flat form

When there are no fields, you place text where it belongs.

Using Preview

1. Open the PDF and click the Markup button.
2. Click the Text tool (a "T" in a box) to add a text box.
3. Drag the box onto the line, type your answer, and adjust the font size from the format controls.
4. Repeat for each line and save.

Using Adobe Reader Fill & Sign

1. Open Fill & Sign.
2. Click where you want to type and enter your text.
3. Use the small toolbar to resize text, or to add checkmarks and crosses for boxes.
4. Save the file.

Using our Add text tool

Add text to PDF lets you place text boxes anywhere on any page, with your choice of size and color, all within your browser.

1. Open the tool and add your form.
2. Click on the page where the first answer goes and type.
3. Adjust the font size to match the printed form, which often uses 10 to 12 point text.
4. Continue for every field, then download.

Tips for neat results on flat forms

• Zoom in while placing text so baselines line up with the printed lines.
• Use one consistent font size throughout, which looks tidier than mixing sizes.
• Type an X for checkboxes, centered in each box.
• Keep answers within the lines. If a field is too short, abbreviate or attach a separate page, following the form's instructions.
• Make scanned forms searchable if needed. Running OCR PDF is not required for filling, but it helps if you want to search the completed file later.

Signing the form

Many forms end with a signature line. Complete all other fields first, then add your signature with Sign PDF, which lets you draw, type or upload a signature and place it on the line. If the form includes a certificate-based signature field and the issuer requires a digital signature, follow their instructions instead.

Saving and sending without losing your answers

The most common frustration with PDF forms is sending a file and hearing that it arrived blank. A few causes and fixes:

• The form was not saved. Some viewers show your entries on screen but require an explicit save or download. Always reopen the saved file to confirm.
• The recipient's viewer does not show field values. Rare, but it happens with unusual forms. Flattening solves it, because answers become part of the page. You can flatten while filling, or afterward with Flatten PDF.
• Printing to PDF dropped the fields. If you used Print to PDF, check the output. Flattening beforehand is more predictable.
• The form is XFA. Use Adobe Reader or request a standard version, as described above.

Should you flatten

Flatten when:

• You are submitting a final version.
• You want to reduce the chance of accidental or deliberate changes.
• You will merge the form with other documents, since field names from different forms can collide.

Do not flatten when:

• The recipient needs to extract field data automatically.
• You expect to make corrections later. Keep an unflattened copy in that case.

Privacy considerations

Forms tend to collect the most sensitive information you have: identification numbers, health details, financial data. When choosing a tool, check whether it uploads your file. Built-in viewers and in-browser tools that process locally avoid sending your answers to a third-party server. After submitting, consider where copies are stored and delete drafts you no longer need.

Key takeaways

• Fillable forms have interactive fields; flat forms need text placed on top; XFA forms often require Adobe Reader.
• Browsers, Preview and Adobe Reader can all fill standard fillable forms for free.
• Our Fill PDF form tool completes text fields, checkboxes and dropdowns in your browser and can flatten the result.
• For flat forms, use Add text to PDF, Preview's Text tool or Reader's Fill & Sign.
• Reopen the saved file to confirm your answers are there, and flatten final submissions.