BASALT · JOURNAL
Form filling, flattening, and what XFA breaks
Form filling looks simple and has one detail that separates tools that work from tools that produce documents which print blank.
Appearance streams
A form field has a value and a separate visual representation called an appearance stream. Setting the value without regenerating the appearance produces a document where the data is present in the file and invisible on the page, or visible in one viewer and absent in another.
This is the most common form bug, and it usually surfaces when someone prints a filled form and the fields come out empty.
A tool that fills forms through a proper form environment regenerates appearances as a matter of course. One that writes values directly into the file may not.
Flattening
Flattening converts filled fields into ordinary page content. After flattening the values are part of the page rather than form data, so they cannot be edited, cannot be accidentally cleared, and render identically everywhere.
For anything being filed or sent onward, flatten. An unflattened form sent to another party is editable by them, which is rarely what was intended.
There is a redaction consequence too: an unflattened field holds its value as data independent of what the page shows, so redacting the visible area of a form field does not necessarily remove the value.
XFA, and why it matters
XFA is an older XML based Adobe form technology embedded in a PDF wrapper. Acrobat supports it. Most other tools, including Apple's Preview and the majority of third party applications, do not, and opening an XFA form in them shows a message asking you to open it in Acrobat instead.
These forms still circulate, particularly in government and financial contexts. A tool that detects an XFA form and refuses clearly is behaving correctly; one that opens it and silently displays or saves something wrong is not.
If your work involves XFA forms regularly, Acrobat is not optional and no comparison changes that.
Being fair
Acrobat's form capability is far deeper than filling: designing forms with calculations, validation and scripting is a substantial feature set with no equivalent in smaller tools. Filling and flattening is the common case, not the whole of it.
Frequently asked questions
Why does my filled PDF form print blank?
Because the field values were set without regenerating the appearance streams, which are the separate visual representation of a field. The data exists in the file but nothing draws it, so viewers and printers differ on what appears.
Should I flatten a form before sending it?
Yes for anything being filed or sent onward. Flattening converts field values into ordinary page content, so they render identically everywhere and cannot be edited or cleared by the recipient.
Can redaction miss form field values?
Yes, on an unflattened form. The field holds its value as data independently of what the page displays, so covering or redacting the visible area does not necessarily remove the underlying value.
What is an XFA form and why will my PDF app not open it?
XFA is an older XML based Adobe form technology inside a PDF wrapper. Acrobat supports it and most other applications do not, so they show a message directing you to Acrobat. A tool that detects and refuses XFA is behaving correctly; one that silently mishandles it is not.
Doing it in Basalt
Basalt is a native macOS PDF toolkit with eighteen tools in one window: merge, split, compress, OCR, Bates numbering, privilege logs, forms, signing, watermarks, comparison and more. Redaction destroys content rather than covering it, and an independent verifier re-opens every written file and proves the material is gone before the file is saved. If it cannot prove it, nothing is written. A one time $29 licence covers up to three Macs, it is free for the first 24 hours, there is no account, and the engine holds no network entitlement at all, which macOS enforces at the code-signature level. Download it at basaltformac.com.
Redaction that proves itself
Basalt destroys the content you mark, then re-opens the file it wrote and proves the content is gone before it saves anything. Your documents never leave your Mac.