Headers, Footers & Watermarks

Headers and Footers

PDF headers and footers are HTML snippets rendered by the engine's print header/footer layer. They appear on every page and support special tokens that are substituted with page metadata at render time.

Special Tokens

Token	Replaced with
`<span class='pageNumber'></span>`	Current page number
`<span class='totalPages'></span>`	Total number of pages
`<span class='date'></span>`	Current date
`<span class='title'></span>`	Document title
`<span class='url'></span>`	Page URL

Basic Example

string header = """
    <div style="font-size:10px; width:100%; text-align:center; font-family:sans-serif;">
        My Company — Confidential
    </div>
    """;

string footer = """
    <div style="font-size:10px; width:100%; text-align:center; font-family:sans-serif;">
        Page <span class='pageNumber'></span> of <span class='totalPages'></span>
    </div>
    """;

var pdf = await renderer
    .WithHeader(header)
    .WithFooter(footer)
    .RenderUrlAsPdfAsync("https://example.com");

From a File

Pass a file path instead of an HTML string — CobaltPdf detects path separators and reads the file automatically:

var pdf = await renderer
    .WithHeader("templates/header.html")
    .WithFooter("templates/footer.html")
    .RenderUrlAsPdfAsync("https://example.com");

Styling Notes

The header/footer engine has some quirks:

The template is rendered in a separate, narrow context. Use width:100% to span the full page.
External stylesheets and web fonts are not loaded. Use inline styles.
The default margin must be large enough to contain the header/footer — otherwise it will be clipped. Default margins are 1 cm; increase them if needed via WithMargins().
Background colors in headers/footers require -webkit-print-color-adjust: exact.

string colorHeader = """
    <div style="
        font-size:11px;
        width:100%;
        padding:4px 10px;
        background:#1a3c5e;
        color:white;
        -webkit-print-color-adjust:exact;
        font-family:Arial,sans-serif;">
        Acme Corp Internal Report — <span class='date'></span>
    </div>
    """;

Watermarks

Watermarks are HTML overlays injected into the page as a fixed-position div before the PDF is captured. They appear on every page because the overlay is position:fixed and Chromium repeats fixed elements across pages in print mode.

Quick Watermarks (Recommended)

Use the WatermarkOptions.WithText factory method with a predefined WatermarkStyle for common watermark patterns:

using static CobaltPdf.Configuration.PdfOptions;

// One-liner — "DRAFT" in bold red, rotated -45 degrees
var pdf = await renderer
    .WithWatermark(WatermarkOptions.WithText("DRAFT", WatermarkStyle.RedDraft))
    .RenderUrlAsPdfAsync("https://example.com");

WatermarkStyle Presets

Style	Appearance
`SoftGray`	Light gray, 700 weight, -45 rotation, 0.28 opacity
`RedDraft`	Bold red, 900 weight, -45 rotation, 0.30 opacity
`Diagonal`	Dark gray, 600 weight, -45 rotation, 0.20 opacity
`BoldStamp`	Dark centered stamp with border, no rotation, 0.28 opacity

Fluent Customization

Chain fluent helpers onto the factory result to fine-tune position, color, rotation, and opacity:

var pdf = await renderer
    .WithWatermark(
        WatermarkOptions.WithText("CONFIDENTIAL", WatermarkStyle.SoftGray)
                        .WithPosition(WatermarkPosition.TopRight)
                        .WithColor("#e74c3c")
                        .WithOpacity(0.2)
                        .WithRotation(-30))
    .RenderUrlAsPdfAsync("https://example.com");

WatermarkPosition

Value	Placement
`Center`	Centered both vertically and horizontally (default)
`TopLeft`	Top-left corner
`TopCenter`	Top edge, centered horizontally
`TopRight`	Top-right corner
`BottomLeft`	Bottom-left corner
`BottomCenter`	Bottom edge, centered horizontally
`BottomRight`	Bottom-right corner

Fluent Helpers Reference

Method	Description
`WithPosition(WatermarkPosition)`	Set position using a single enum value
`WithColor(string cssColor)`	Override text color (any CSS value, e.g. `"#ff0000"`, `"red"`)
`WithRotation(int degrees)`	Set rotation angle (-45 = counter-clockwise)
`WithOpacity(double)`	Set opacity from 0.0 (invisible) to 1.0 (opaque)
`WithHtml(string html)`	Replace generated HTML with a fully custom snippet
`WithRasterize(bool enable = true)`	Flatten the watermark to an image baked into every page — see Rasterized watermarks

Custom HTML Watermark

For full control, pass raw HTML directly:

var pdf = await renderer
    .WithWatermark(new WatermarkOptions
    {
        Html       = "<div style='font-size:72pt; font-family:sans-serif; color:red;'>DRAFT</div>",
        Rotation   = -45,
        Opacity    = 0.15,
        Vertical   = VerticalAlignment.Middle,
        Horizontal = HorizontalAlignment.Center
    })
    .RenderUrlAsPdfAsync("https://example.com");

WatermarkOptions Properties

Property	Type	Default	Description
`Html`	`string`	`""`	HTML markup rendered inside the watermark container
`Rotation`	`int`	`0`	Rotation in degrees. Negative = counter-clockwise
`Opacity`	`double`	`0.5`	`0.0` = transparent, `1.0` = fully opaque
`Vertical`	`VerticalAlignment`	`Middle`	`Top`, `Middle`, or `Bottom`
`Horizontal`	`HorizontalAlignment`	`Center`	`Left`, `Center`, or `Right`
`Color`	`string?`	`null`	CSS color override applied to all watermark text
`Rasterize`	`bool`	`false`	Flatten the watermark to an image baked into every page — see Rasterized watermarks

Image Watermark

// Base64-encode a PNG and embed it directly
string base64Logo = Convert.ToBase64String(File.ReadAllBytes("logo.png"));

var pdf = await renderer
    .WithWatermark(new WatermarkOptions
    {
        Html     = $"<img src='data:image/png;base64,{base64Logo}' style='width:300px;' />",
        Rotation = 0,
        Opacity  = 0.1,
        Vertical = VerticalAlignment.Middle,
        Horizontal = HorizontalAlignment.Center
    })
    .RenderUrlAsPdfAsync("https://example.com");

Trial Watermark

When running without a valid license, CobaltPdf automatically overlays a COBALT PDF TRIAL watermark on every page. Activate a license to remove it — see Licensing.

The trial watermark and any user-defined watermark can coexist; user watermarks are rendered on top.

Rasterized watermarks

By default, watermarks are injected as selectable text/vector content — which means anyone with a PDF editor can select the watermark text and delete it. The opt-in WatermarkOptions.Rasterize property (fluent: .WithRasterize(bool enable = true)) flattens the watermark to a high-resolution image baked into every page instead, so it can't be removed with a PDF editor's "edit text → delete".

var pdf = await renderer
    .WithWatermark(
        WatermarkOptions.WithText("CONFIDENTIAL", WatermarkStyle.SoftGray)
                        .WithRotation(-45)
                        .WithOpacity(0.3)
                        .WithRasterize())
    .RenderUrlAsPdfAsync("https://example.com");

The default is false — existing watermark behaviour is completely unchanged unless you opt in. The flag and behaviour are identical in both the Chromium (CobaltPDF) and WebKit (CobaltPDF.WebKit) libraries.

Important

Rasterization is tamper-resistance, not DRM. A baked-in image is much harder to remove than selectable text, but a determined user can still crop or paint over page pixels. Do not rely on it as an unremovable mark.

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