renderToPdf

The primary entry point for PDF generation. Four overloads: auto-paginating and manual multi-page, each with ByteArray and OutputStream variants.

Auto-paginating (default) 

fun renderToPdf(
    config: PdfPageConfig = PdfPageConfig.A4,
    density: Density = Density(2f),
    mode: RenderMode = RenderMode.VECTOR,
    defaultFontFamily: FontFamily? = InterFontFamily,
    pagination: PdfPagination = PdfPagination.AUTO,
    content: @Composable () -> Unit,
): ByteArray

Renders Compose content to a PDF, automatically splitting across pages when content overflows.

With PdfPagination.AUTO (the default), direct children of content are treated as “keep-together” units — if a child would straddle a page boundary, it is pushed to the next page. A single child taller than a page flows continuously across pages.

Parameters

Parameter Type Default Description
config PdfPageConfig PdfPageConfig.A4 Page size and margins
density Density Density(2f) Pixel resolution for Compose layout. Each PDF point maps to density x density pixels. Higher values improve anti-aliasing (especially for raster mode) at the cost of memory
mode RenderMode RenderMode.VECTOR Vector (SVG-based) or raster rendering
defaultFontFamily FontFamily? InterFontFamily Font family for the default text style. When non-null, content is wrapped so both Compose and PDFBox use the same font. Pass null for system fonts
pagination PdfPagination PdfPagination.AUTO Controls page splitting. AUTO automatically paginates. SINGLE_PAGE clips to one page
content @Composable () -> Unit – The composable content to render

Returns

ByteArray – a valid PDF document (one or more pages).

Throws

Exception When
Compose2PdfException Rendering fails (wraps the underlying cause)
IllegalArgumentException Precondition failures (not wrapped)

Example 

val pdfBytes = renderToPdf(
    config = PdfPageConfig.LetterWithMargins,
    mode = RenderMode.VECTOR,
) {
    // Direct children are "keep-together" units
    ReportHeader()
    DataTable(items)       // kept together on one page
    SummarySection()       // pushed to next page if needed
}
File("report.pdf").writeBytes(pdfBytes)

Auto-paginating (OutputStream) 

fun renderToPdf(
    outputStream: OutputStream,
    config: PdfPageConfig = PdfPageConfig.A4,
    density: Density = Density(2f),
    mode: RenderMode = RenderMode.VECTOR,
    defaultFontFamily: FontFamily? = InterFontFamily,
    pagination: PdfPagination = PdfPagination.AUTO,
    content: @Composable () -> Unit,
)

Streaming variant – writes the PDF directly to outputStream without creating an intermediate ByteArray. The stream is not closed by this function.

Parameters and behavior are identical to the ByteArray variant above.

Example 

// Ktor
call.respondOutputStream(ContentType.Application.Pdf) {
    renderToPdf(this, config = PdfPageConfig.A4WithMargins) {
        ReportContent(data)
    }
}

// File
FileOutputStream("report.pdf").use { out ->
    renderToPdf(out) { ReportContent(data) }
}

Multi-page 

fun renderToPdf(
    pages: Int,
    config: PdfPageConfig = PdfPageConfig.A4,
    density: Density = Density(2f),
    mode: RenderMode = RenderMode.VECTOR,
    defaultFontFamily: FontFamily? = InterFontFamily,
    content: @Composable (pageIndex: Int) -> Unit,
): ByteArray

Renders multiple pages of Compose content to a single PDF. The page count must be known upfront.

Parameters

Parameter Type Default Description
pages Int – Number of pages to render (must be positive)
config PdfPageConfig PdfPageConfig.A4 Page size and margins (applied uniformly to all pages)
density Density Density(2f) Pixel resolution for Compose layout
mode RenderMode RenderMode.VECTOR Vector or raster rendering
defaultFontFamily FontFamily? InterFontFamily Default font family
content @Composable (pageIndex: Int) -> Unit – Content for each page. Receives the zero-based page index

Returns

ByteArray – a valid multi-page PDF document.

Throws

Exception When
Compose2PdfException Rendering fails
IllegalArgumentException pages is not positive

Example 

val totalPages = 3
val pdfBytes = renderToPdf(
    pages = totalPages,
    config = PdfPageConfig.A4WithMargins,
) { pageIndex ->
    Column(Modifier.fillMaxSize()) {
        Text("Page ${pageIndex + 1} of $totalPages")
        when (pageIndex) {
            0 -> CoverPage()
            1 -> DataPage()
            2 -> SummaryPage()
        }
    }
}

Multi-page (OutputStream) 

fun renderToPdf(
    outputStream: OutputStream,
    pages: Int,
    config: PdfPageConfig = PdfPageConfig.A4,
    density: Density = Density(2f),
    mode: RenderMode = RenderMode.VECTOR,
    defaultFontFamily: FontFamily? = InterFontFamily,
    content: @Composable (pageIndex: Int) -> Unit,
)

Streaming variant of the multi-page API. Writes the PDF directly to outputStream. The stream is not closed by this function.

Parameters and behavior are identical to the ByteArray multi-page variant above.

Example 

call.respondOutputStream(ContentType.Application.Pdf) {
    renderToPdf(this, pages = 3, config = PdfPageConfig.A4WithMargins) { pageIndex ->
        PageContent(pageIndex)
    }
}

Thread safety

Both overloads are not thread-safe. Concurrent calls should be serialized externally (e.g., via a Mutex or single-threaded Dispatchers).

See also