Edit a PDF: change existing text, type Thai and fill in PDF forms for free

You have a PDF form and don’t want to print it and write by hand, or you need to add a name, a date or a logo to a PDF. Here is the difference between fillable and scanned forms, how to type Thai onto a PDF, and a warning about “deleting” text.

In short

• The form has fields: use fill PDF form to type Thai into fields, tick boxes and pick options.
• Changing words in a document: use edit PDF, tap the line and retype it.
• A scanned form or any other PDF: the same tool places text anywhere, adds a picture or logo, highlights, draws boxes and writes with a pen.
• Hiding confidential data: don’t cover it with white; use redact PDF.

Every tool runs in your browser. Your file is not uploaded.

Fillable forms vs flat forms

• Fillable (interactive) forms: the PDF 1.7 specification calls them AcroForms, a collection of fields for gathering information from the user. Adobe says they have highlighted fields such as text fields, checkboxes or radio buttons.
• Flat forms: Adobe describes these as scanned paper forms or PDFs with no interactive fields, where you add text boxes yourself.

Thai examples: we opened the 2569 ภ.ง.ด.94 form from the Revenue Department’s forms page and found it is a fillable form; several Social Security Office forms we checked were flat, with no fields. The Revenue Department’s own FAQ says that if you can’t type and the pointer is a hand, that form is still being prepared, but you can download it to use instead of the paper form.

Filling in a fillable form

1. Open fill PDF form and choose the file.
2. Type Thai into the fields, tick boxes and pick options.
3. Save it as a filled-in PDF.

The result has its fields flattened into page content, as described in the PDF-LIB documentation. It no longer has interactive fields, but this is not a password lock or a guarantee that the document cannot be edited. Keep the original form for corrections and check the downloaded copy before sending. Read why filled PDF fields are no longer editable.

Typing onto a scanned form or any PDF

1. Open edit PDF and choose the file.
2. Pick the text tool, tap where you want the text, type Thai in the side panel, then use the select tool to drag it onto the line (one box per line).
3. Add a picture or logo, highlight, draw a box or write with the pen as needed.
4. Download the new file.

To sign it as well, use sign PDF, and read about electronic signatures in Thailand.

Editing the existing text

1. Open edit PDF and choose the file. The Edit text tool is already selected.
2. Tap a line with a dashed outline. A box appears under it with the current words.
3. Just type. Size, colour and typeface are matched to the original as closely as possible, and you can adjust size, weight and typeface on the right.
4. Save the PDF and download it.

How it works: Microsoft explains that PDF is a fixed format: it stores where text, pictures and graphics sit on a page, but not necessarily how they relate, and even in Adobe Acrobat editing text in its original font needs that font on your computer. So our tool covers the old line with the paper’s colour and puts the new text on top. The type is close to the original, not always identical.

Limits

• One line at a time; if a line gets much longer, the lines after it don’t move.
• Scanned pages have no text to tap: use white-out and type over it instead.
• Rewriting whole paragraphs: convert with PDF to Word, edit in Word and save a new PDF. Microsoft warns the converted file may not look exactly like the original, and pages that are mostly charts or pictures may come through as images whose text can’t be edited.

Covering text doesn’t delete it

Both editing a line and white-out put colour on top so the old text can’t be seen; it is still underneath and can be copied out.

• The NSA says covering text with black boxes works for paper but in general is not effective for computer documents, and is the most common mistake.
• The U.S. Court of Federal Claims explains that a black box laid over data merely hides it: anyone can copy the box into a word processor and see the text underneath.

For confidential data such as ID card or account numbers, use redact PDF, which removes the text under the black bars from the file.

Note

This article is based on Adobe, Apple and Microsoft help pages, Adobe’s edition of the PDF 32000-1:2008 specification (copy in the Internet Archive), documents from the NSA (copy in the Internet Archive) and the U.S. Court of Federal Claims, and the Revenue Department website, read on 30 September 2026. Whether each form has fields comes from our own check of the files that day.

The form-output section was reviewed on 1 November 2026 against the tool implementation and PDF-LIB documentation, correcting the distinction between flattening and a password lock.