Level 0: PdfFileWriter

Level 0 is the raw PDF object model and byte-level file emitter. Every type defined in ISO 32000-2:2020 has a corresponding PHP class with typed properties matching the spec fields.

When to use Level 0

• Building a library or framework on top of phpdftk
• Emitting PDF features not yet exposed by higher levels
• Manipulating the object graph directly (e.g., custom annotation types)
• Learning the PDF specification interactively

Architecture

PdfFileWriter (byte emitter)
  ├── ObjectRegistry (assigns object numbers)
  ├── CrossReferenceTable (20-byte xref entries)
  └── TrailerDictionary (/Size, /Root, /Info, /ID, /Encrypt)

Catalog ─── PageTree ─── Page ─── ContentStream
                                  Resources
                                  Annotations

Example: minimal PDF

use Phpdftk\Pdf\Core\File\PdfFileWriter;
use Phpdftk\Pdf\Core\Document\{Catalog, Page, PageTree};
use Phpdftk\Pdf\Core\Content\{ContentStream, Resources};
use Phpdftk\Pdf\Core\Font\{Type1Font, StandardFont};
use Phpdftk\Pdf\Core\{PdfArray, PdfNumber, PdfReference};

$fw = new PdfFileWriter();

$catalog = new Catalog();
$fw->setCatalog($catalog);

$pageTree = new PageTree();
$fw->register($pageTree);
$catalog->pages = new PdfReference($pageTree->objectNumber);

$page = new Page();
$fw->register($page);
$page->parent = new PdfReference($pageTree->objectNumber);
$page->mediaBox = new PdfArray([
    new PdfNumber(0), new PdfNumber(0),
    new PdfNumber(612), new PdfNumber(792),
]);
$page->resources = new Resources();

$pageTree->kids = [new PdfReference($page->objectNumber)];
$pageTree->count = 1;

$font = new Type1Font(StandardFont::Helvetica);
$fw->register($font);
$page->resources->addFont('F1', $font);

$cs = new ContentStream();
$fw->register($cs);
$cs->beginText()
   ->setFont('F1', 12)
   ->moveTextPosition(72, 720)
   ->showText('Hello from Level 0')
   ->endText();

$page->contents = [new PdfReference($cs->objectNumber)];

$fw->save('level0.pdf');

Object model overview

Every PdfObject subclass has:

• A PDF_TYPE constant matching the spec’s /Type value
• Public properties matching spec fields in camelCase
• A toPdf(): string method that serializes to PDF syntax
• An objectNumber assigned by the ObjectRegistry when registered

Primitive types

Class	PDF syntax
PdfName	/Name
PdfString	(text) or <hex>
PdfNumber	42 or 3.14
PdfBoolean	true / false
PdfNull	null
PdfArray	[1 2 3]
PdfDictionary	<< /Key /Value >>
PdfReference	5 0 R
PdfStream	Stream with dictionary + binary data

ContentStream operators

The ContentStream class has fluent methods for all 69 PDF content operators:

$cs->saveGraphicsState()           // q
   ->setFillColorRGB(1, 0, 0)     // rg
   ->rectangle(72, 72, 100, 50)   // re
   ->fill()                        // f
   ->restoreGraphicsState();       // Q