File formats
What Nixt PDF opens and saves, what it reads inside a PDF, what it keeps unchanged when you edit, and which operations rewrite the whole file.
What Nixt PDF opens
Nixt PDF opens PDF documents (.pdf) and nothing else. It looks at what a file contains, not only its name:
- A Word document, spreadsheet or presentation — even one named
.pdf— isn’t opened. The message names the Nixt Office app that opens it: Nixt Writer, Nixt Sheets or Nixt Slides.
It also makes new PDFs from PNG and JPEG pictures; see Making a PDF from pictures.
What it reads inside a PDF
| Part of a PDF | Support |
|---|---|
| Pages | Displayed and printed for any PDF the built-in renderer can draw. |
| Text | Read for searching, selecting, copying, editing and redacting, including text in embedded and standard fonts, two-byte fonts, and text drawn inside reusable parts of a page. Punctuation, accents and ligatures are read as the characters they stand for. |
| Pages turned on their side | Text is read in the order a person reads it. |
| Password protection | AES-256, AES-128, and 128-bit and 40-bit RC4, with either password. See Passwords and security. |
| Bookmarks | Read, followed, added, renamed and deleted. |
| Printed page numbers | Read and set. |
| Links | Followed (web, email and inside the document), listed and removed. |
| Form fields | Text, tick boxes, choices, lists, signature fields and buttons. Text, tick boxes, choices and lists can be filled in. |
| Form calculations | The standard sum, product, average, smallest and largest calculations, with number formats. |
| Comments | Shown, and listed in the Comments view with their replies and review statuses. Nixt PDF adds highlights, underlines, strike-throughs, squiggles, notes, freehand drawing, text boxes, callouts, insertion marks, rectangles, ovals, lines, arrows, clouds and stamps, each with its own appearance, and writes replies and statuses. |
| Stamps | Standard named stamps, stamps with their own drawing, and stamps without a drawing (which can be given one). |
| Digital signatures | Checked. See Validating signatures. |
| Layers | Listed, shown and hidden. |
| Attached files | Listed, saved, added and removed. |
| Opening behaviour | Page layout and full screen are honoured; all settings are read and can be set. |
| Metadata | Properties, custom properties and XMP are read; properties and custom properties can be changed. |
| Tagged structure for screen readers | Detected and kept. |
| Scripts | Detected and never run. They can be removed. |
Damaged and unusual files
A damaged file is refused with a message, such as This file isn’t a readable PDF. It may have been damaged in transit., rather than half-opened. Parts of a file built to be unreasonably large or deeply nested are not read, so the rest of the document still opens safely.
What is kept when you edit
Almost every change is added to the end of the file as a new revision. Everything you didn’t change stays exactly as it was, byte for byte — including parts of the PDF that Nixt PDF doesn’t understand. That is why:
- a digital signature stays intact when you fill in a form or add a comment afterwards;
- Undo can take a change back by removing the last revision;
- the Revisions in the file count in Document properties goes up as you work.
The document’s Produced by property isn’t changed.
Operations that rewrite the whole file
Some jobs must not leave the old version inside the file. These rewrite the document as a single revision containing only what is left:
| Operation | Why it rewrites |
|---|---|
| Redaction | So the removed words don’t survive in an earlier revision. |
| Password…, Change password… | So no unprotected copy of the pages is left in the file. |
| Remove the password | So no protected copy is left in the file. |
| Hidden content… › Take it out | Because most hidden content is in earlier revisions. |
| Reduce the size… › Make it smaller, and shrinking pictures | To drop earlier revisions and unused objects. |
| Save pages as a PDF… | So the pages you left out aren’t hidden inside the new file. (The open document isn’t changed.) |
Rewriting clears the undo history, breaks existing digital signatures, and keeps a document’s password protection unless you removed it.
Files Nixt PDF writes
| File | Format |
|---|---|
| Documents, page ranges, comment summaries, signed versions | |
| Text, comments, comparison reports | Plain text (UTF-8) |
| Form answers | CSV, with Field, Question and Answer columns |
| Web page | HTML, with its styling included |
| Page pictures | PNG, JPEG or TIFF |
| Digital IDs | PKCS#12 (.p12), protected with AES — or triple DES when you ask for older software |
| Certificates | DER-encoded certificate (.cer) |
| Stamp sets | A stamp set file containing stamp designs and pictures; it holds nothing that runs |
A summary of comments is a new A4 document set in the standard PDF fonts.
Files Nixt PDF reads besides PDFs
| File | Used by |
|---|---|
| PNG, JPEG | Make one from pictures, Add picture, Replace… in All pictures |
| Picture files | Picture signatures and picture stamps |
| CSV, XFDF | Fill in from a file… |
| Any file | Attach a file… (up to 64 MB) |
.p12, .pfx | Signing with a digital ID |
.cer, .crt, .pem | Trusted certificates › Add a certificate… |
| Stamp set files | Add stamps from a file… (up to 48 MB) |
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