everyday mac tools

Fill in a PDF form on a Mac and flatten it so it stays filled

· 5 min read

Fill the form in Preview by clicking each field and typing. Then, instead of saving, print it: File, Print, and choose Save as PDF from the PDF menu in the bottom-left corner of the print dialog. The file that comes out has your answers drawn onto the page as ordinary content, which is what “flattened” means.

Everything else in this post is about why that second step matters, and what to do when the form does not behave.

Fill the form in Preview

Preview has handled PDF forms for years, and for most forms it is all you need.

  1. Open the PDF in Preview. If the document has real form fields, Preview highlights them when you move the pointer over the page, and a banner may offer to help you fill it in.
  2. Click a field and type. Tab moves to the next field. Checkboxes and radio buttons toggle with a click.
  3. For a signature line, use the Markup toolbar (the pen-tip icon) and the Signature tool. Sign a PDF on a Mac covers creating one with the trackpad, the camera or an iPhone.
  4. Save with Command-S. Preview writes your values back into the form fields.

That saved file is fine to keep. It is not always fine to send, and the next section explains why.

Why a filled form can open empty somewhere else

A PDF form is two things layered on top of each other: the page, and a set of fields that float above it. When you type into a field, the value is stored with the field, not painted onto the page. A reader then has to draw the value in the right place.

Most readers do this well. Some do not, and a form filled in one app has a long history of opening in another with every field apparently blank, because the value is present in the file but the reader has not been told how to display it. The person receiving it sees an empty form and assumes you never filled it in.

There are two other reasons to flatten before sending:

  • The fields stay editable. Anyone who opens the file can change a number or a name and save it. For an agreement, a claim or an application, you want the copy you sent to be the copy that exists.
  • The form structure comes along. Field names, default values, calculation scripts and sometimes the form author’s notes travel with the file. None of it is needed once the answers are final.

Flattening removes all three problems at once, because there are no fields any more, only a page with text on it.

Flatten it with the print dialog

macOS does not have a button labelled Flatten. It has something better hidden in plain sight: the print path draws the page exactly as it appears on screen, fields and all, and can save that drawing as a new PDF.

  1. With the filled form open in Preview, choose File, Print (Command-P).
  2. Leave the printer as it is; you are not going to use it. Check that the page range covers the whole document.
  3. In the bottom-left corner of the print dialog, open the PDF menu and choose Save as PDF.
  4. Give it a new name. Keep the original, filled but unflattened, in case you need to correct something later.
  5. Click Save.

Open the result. Clicking where a field used to be does nothing, because the field is gone. The text is still text, so you can select it and search it; it is simply part of the page now.

What you lose in the process: clickable links become plain text, bookmarks and the table of contents disappear, and any attachments inside the PDF are not carried over. For a completed form, none of that is usually a loss. If the form has a hyperlink that matters, mention it in the email instead.

Check the result before you send it

Two minutes, and it removes the most common surprise.

  1. Open the flattened file in a second viewer if you have one. Quick Look in Finder (select the file and press Space) uses a different code path from Preview and is a fair check.
  2. Look at every page. A field that was filled but not displayed in the source can also fail to display when printed.
  3. Try to click into a field. Nothing should happen.
  4. Select All (Command-A) and look at what highlights. Your answers should be included; if they are not, the print produced an image rather than text, which usually means the source was a scan.

If the file is going somewhere that also needs your author name, creation date and editing history removed, Remove metadata from a PDF on a Mac before you share it covers that. Printing to PDF does not clear it; the new file gets a fresh title and creator, and sometimes that is enough, and sometimes it is not.

When the form is not really a form

Plenty of “forms” are scans or exports with lines drawn where the answers go and no fields at all. Preview cannot fill those in the normal way, but it can put text on them.

  1. Open the Markup toolbar and choose the Text tool (the box with a T).
  2. A text box appears in the middle of the page. Type your answer and drag the box into position over the line.
  3. Adjust the font and size from the Markup toolbar so it matches the form.
  4. Repeat for each answer, then print to PDF as above so the boxes become part of the page.

It is slower than a real form and there is no Tab key, but the result is the same flattened page.

On recent versions of macOS, Preview also tries to detect fields on forms that do not declare any, and offers a text box when you click on a line. When it works, it saves the dragging. When it guesses wrong, switch back to the Text tool.

When you fill forms for a living

For one form a month, Preview plus the print dialog is the whole answer. If you work through a stack of them, the same two-step routine starts to cost time, and the check for “did the values survive” becomes something you skip.

Basalt has a Forms tool that fills a form and locks it so the values stay where you put them, in a single step, and writes the result as a new file so the blank original is never touched. It is one of eighteen PDF tools in the same window, which matters if the next step is usually adding a signature, a watermark or a page number. Everything happens on the Mac; nothing is uploaded. It is a paid app after a 24-hour free trial, and for a single form it is not a better answer than the print dialog.

Questions

Does flattening stop someone editing the form? No. It removes the fields, so the easy way of changing a value is gone, but the text on the page is still text, and a PDF editor can alter it. Flattening protects you from accidental changes and from readers that hide field values. It does not make the document tamper-proof. Keep your own copy of what you sent.

Does Export as PDF in Preview flatten the form? No. File, Export keeps the form fields intact and editable, which is useful when you want to hand a partly completed form to someone else to finish. Only the print route flattens.

Can I unflatten a form later? No. The fields are gone. This is why the steps above have you keep the filled, unflattened version under a different name.

Will printing to PDF reduce the quality? Text and vector graphics come through unchanged. Scanned pages and photos may be re-encoded, and the file can end up either larger or smaller than the original. If a scan looks softer afterwards, use the original filled file for your records and the flattened one for sending.