PDF API

A PDF document is organized as a sequence of pages. Each page can contain several types of content: paragraphs, tables, drawings (images, shapes, charts), annotations, and interactive form fields.

The core content elements are:

• Paragraph (ApiParagraph) — a block of text. Paragraphs consist of one or more runs (ApiRun), each of which carries the text itself and its character formatting (font, size, bold, italic, color, etc.).
• Table (ApiTable) — a grid structure whose cells (ApiTableCell) contain document content (paragraphs).
• Drawing (ApiDrawing) — an image, shape, or chart placed at a specific position on the page.

Pages and their content are accessed through the document (ApiDocument) and page (ApiPage) objects.

Annotations

Annotations let you mark up PDF content without modifying it. The PDF API supports the following annotation types:

Category	Types
Note/text	ApiTextAnnotation, ApiFreeTextAnnotation
Markup	ApiHighlightAnnotation, ApiUnderlineAnnotation, ApiStrikeoutAnnotation, ApiCaretAnnotation
Shapes	ApiSquareAnnotation, ApiCircleAnnotation, ApiLineAnnotation, ApiPolyLineAnnotation, ApiPolygonAnnotation
Other	ApiInkAnnotation, ApiStampAnnotation, ApiRedactAnnotation

All annotation types share a common base (ApiBaseAnnotation) that provides border, fill, opacity, author, date, and reply properties.

Form fields and widgets

PDF forms include fields and widgets. A field defines the data model (name, value, validation rules), while a widget determines the visual representation of a field.

Field type	Widget
ApiTextField	ApiTextWidget
ApiCheckboxField	ApiCheckboxWidget
ApiRadiobuttonField	—
ApiComboboxField	—
ApiListboxField	—
ApiImageField	—
ApiDateField	—
ApiButtonField	ApiButtonWidget

Creating a new PDF document

To create a PDF document with ONLYOFFICE Document Builder, you first create a document in an editable format (DOCX) and then save it as PDF. The simplest example creates a single page with centered "Center" text:

// create a document file with ONLYOFFICE Document Builder
builder.CreateFile("docx");

// create a new 'oDocument' variable and get the created document
const oDocument = Api.GetDocument();

// create a new paragraph for the document content
const oParagraph = Api.CreateParagraph();

// set the paragraph justification to center the text
oParagraph.SetJc("center");

// add a text containing a single 'Center' word to the paragraph
oParagraph.AddText("Center");

// push the paragraph to the document
oDocument.Push(oParagraph);

// save the resulting document as a PDF file with the 'example.pdf' name and close it
builder.SaveFile("pdf", "example.pdf");
builder.CloseFile();

The document initializes with a default page configuration. You can customize page size, orientation, and margins using the appropriate page configuration methods.

Opening an existing PDF document

To edit an existing PDF document, open it with builder.OpenFile, then get its pages and modify their content:

// use a path or URL to an existing 'mydocument.pdf' file to open it with ONLYOFFICE Document Builder
builder.OpenFile("https://example.com/mydocument.pdf");

// create a new 'oDocument' variable and get the opened PDF document contents
const oDocument = Api.GetDocument();

// get the first page
const oPage = oDocument.GetElement(0);

// create and configure a new paragraph
const oParagraph = Api.CreateParagraph();
oParagraph.SetJc("center");
oParagraph.AddText("Center");

// add the paragraph to the page
oPage.Push(oParagraph);

// save the resulting PDF document as a file in the .pdf format with a new 'example.pdf' name and close it
builder.SaveFile("pdf", "example.pdf");
builder.CloseFile();

Use the appropriate API documentation sections to find out which methods allow you to change certain PDF document element formatting properties and work with PDF-specific features.