HTML output

byte[] html = document.RenderAsHtml();
File.WriteAllBytes("invoice.html", html);

HTML output is a single self-contained file: semantic markup, a deduplicated <style> block, and images embedded as base64 data: URIs. Nothing links out, so you can email it, drop it into a web page, or open it straight from disk.

It is a reflowable document, not a picture of a printed page. Text wraps to the reader’s window, and the browser paginates when printing. If you need an exact fixed-page rendering, use PDF.

What the file looks like

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<title>Quarterly Report</title>
<style>
@page{size:595pt 842pt;margin:36pt 36pt 36pt 36pt}
.pp-page{width:595pt;padding:36pt 36pt 36pt 36pt}
.pp-t1{font-size:18pt;font-weight:700}
</style>
</head>
<body>
<div class="pp-doc">
<div class="pp-page">
<header class="pp-band pp-band-header"><p>Acme Ltd</p></header>
<div class="pp-body">
<p class="pp-p1"><span class="pp-t1">Quarterly Report</span></p>
</div>
</div>
</div>
</body>
</html>

Every class carries a pp- prefix, so the markup will not collide with a host page’s styles if you lift the body out. Styles are deduplicated: a style used on a thousand runs is written once.

Elements that use only the defaults carry no class at all - the reset already encodes them (10pt Arial, a 1.2 line-height, 4pt cell padding, a 24pt list indent), because those are the same values the layout engine uses.

Page size and margins

Page setup maps twice - a container width for the screen, and an @page rule for printing:

doc.PageSize(PageSize.A4).Margin(36f);

On screen you get a 595pt-wide page-shaped container. When the reader prints (or saves to PDF from the browser), @page supplies the sheet size and margins, and the container’s own padding is reset so the two never add up. A document without a PageSize gets a plain 800pt-wide container and no @page rule at all.

Sections each become their own container with their own named @page, so a landscape appendix prints landscape.

Printing to PDF from the browser

Open the file and print. The @page rule gives the correct sheet size and margins, <thead> and <tfoot> rows repeat on every page, and page breaks and keep-together hints are honored via break-before / break-inside.

This is a convenience, not a replacement for OutputFormat.Pdf - the browser wraps text with its own font metrics, so line breaks and page counts differ from Papyra’s PDF output.

What HTML does better than the other formats

• Real font weights. FontWeight.Light through BLACK map to CSS font-weight: 300…900. DOCX and XLSX collapse everything to a bold flag.
• True alpha. Translucent colors emit rgba(). DOCX has no alpha channel and blends onto white.
• Repeating table footers. <tfoot> repeats on every printed page; OOXML has no equivalent, so DOCX can only repeat headers.
• Per-sub-list numbering. Each nested list keeps its own format. Word allows one configuration per level within a numbering definition, so DOCX cannot express sibling sub-lists that differ.

Limitations

• Headers and footers render once per section, at the top and bottom of the flow - not repeated on every printed page. One container per printed page is not possible: the browser re-wraps with its own metrics, so Papyra’s page breaks would put content in the wrong container.
• Page-number fields are omitted. A reflowable document has no page count, and the CSS Paged Media counters that could supply one when printing are not implemented by Chrome or Firefox. A PageXofY() footer therefore renders its literal text without the numbers - in bands and in body paragraphs alike. RenderDate() works normally - it has a definite value.
• Custom fonts are named, not embedded. Fonts registered with RegisterFont are embedded in PDF output only; HTML emits the family name with an Arial fallback, so install the font or use a web font in the host page. See fonts.
• File size. A 2 MB logo becomes roughly 2.7 MB of base64. Self-contained output is the trade-off.
• Adjacent cell borders collapse. A cell without its own left border still shows its neighbour’s right border, and when two cells give a shared edge different styles the browser picks one by CSS precedence (dashed beats dotted beats solid at equal widths). PDF strokes each edge independently.
• Watermarks stamp once per section container, and an auto-sized watermark’s font size is approximated (the browser cannot be asked to measure text before layout).
• There are no HTML-specific render options yet.