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Use SelectPdf’s HtmlToPdf class: call ConvertUrl for a web address or ConvertHtmlString for markup, save the returned PdfDocument, and close it. For HTML that uses relative images or stylesheets, pass a base URL so SelectPdf can resolve those assets.
Choose the SelectPdf package before writing code
SelectPdf is distributed through NuGet. The current installation guidance lists Select.HtmlToPdf.NetCore for modern .NET (including .NET 5 through .NET 10 and supported .NET Core/.NET Standard targets) and Select.HtmlToPdf for legacy .NET Framework 2.0–4.5. The vendor’s .NET Core guidance is Windows-specific; it does not run on Linux or macOS. Confirm the package version and operating-system support for your deployment before committing to an architecture.
- In Visual Studio, open Tools → NuGet Package Manager → Manage NuGet Packages for Solution, or run
dotnet add package Select.HtmlToPdf.NetCorefor a modern .NET project. - Install one main SelectPdf package only. If you choose the Blink or Chromium engine, add the matching companion package documented for that version. WebKit is the default bundled option.
- Build and run on the same Windows target class used in production. A conversion that works on a developer workstation does not prove that fonts, permissions, native dependencies, or engine binaries are available on the server.
Convert a URL to PDF
ConvertUrl is the shortest path when the source is already published at an HTTP or HTTPS address.
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using SelectPdf;
var converter = new HtmlToPdf();
var document = converter.ConvertUrl("https://www.example.com");
document.Save("output.pdf");
document.Close();Save can write to a file, stream, memory buffer, or HTTP response. Always close the returned PdfDocument after saving; the API reference says closing releases the system resources used during conversion.
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Returning the PDF from ASP.NET Core
using Microsoft.AspNetCore.Mvc;
using SelectPdf;
[ApiController]
[Route("pdf")]
public class PdfController : ControllerBase
{
[HttpGet("from-url")]
public IActionResult FromUrl([FromQuery] string url)
{
if (!Uri.TryCreate(url, UriKind.Absolute, out var parsed) ||
(parsed.Scheme != Uri.UriSchemeHttp && parsed.Scheme != Uri.UriSchemeHttps))
return BadRequest("url must be an absolute HTTP or HTTPS URL");
var converter = new HtmlToPdf();
var document = converter.ConvertUrl(parsed.ToString());
using var stream = new MemoryStream();
document.Save(stream);
document.Close();
return File(stream.ToArray(), "application/pdf", "page.pdf");
}
}Validate and restrict destinations in a real service. Accepting arbitrary URLs can turn a PDF endpoint into a server-side request forgery risk. Consider an allowlist, outbound network policy, authentication requirements, and request-size and time limits.
Convert an HTML string
Use ConvertHtmlString when your application generates markup itself, such as an invoice or report.
using SelectPdf;
string html = "<html><body><h1>Invoice 1007</h1><p>Amount: $42.00</p></body></html>";
var converter = new HtmlToPdf();
var document = converter.ConvertHtmlString(html);
document.Save("invoice.pdf");
document.Close();Resolve relative CSS and images with a base URL
Markup such as <img src="images/logo.png"> or <link href="css/site.css"> has no location when supplied as a plain string. Pass a base URL as the second argument:
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using SelectPdf;
string html = @"
<html>
<head>
<link rel='stylesheet' href='css/report.css'>
</head>
<body>
<img src='images/logo.png' alt='Company logo'>
<h1>Monthly report</h1>
</body>
</html>";
var converter = new HtmlToPdf();
var document = converter.ConvertHtmlString(html, "https://www.example.com/reports/");
document.Save("report.pdf");
document.Close();The base URL is used to resolve relative references; it is not a replacement for making those resources reachable. Protect private assets with appropriate authentication or embed them as data where suitable.
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Pick the rendering engine for your page
SelectPdf documents WebKit, WebKit Restricted, Blink, and Chromium engines. These are vendor descriptions rather than independent benchmark results.
| Engine | Documented fit | Deployment note |
|---|---|---|
| WebKit | Default option; suitable for ES5 JavaScript and classic CSS. | Bundled default; verify behavior with your pages. |
| WebKit Restricted | WebKit variant documented by SelectPdf. | Check the vendor’s restrictions and version guidance. |
| Blink | Modern HTML/CSS and ES6 JavaScript on supported modern targets. | Install the matching Blink companion package when required. |
| Chromium | Modern HTML/CSS and JavaScript. | Distributed through a separate Chromium.Windows NuGet companion package. |
Engine and package compatibility is version-sensitive. Check the official engine and installation documentation for your target framework and host, then render representative pages in the intended environment. Inspect pagination, fonts, images, and JavaScript-driven sections rather than assuming browser-perfect output.
URLs, strings, and dynamic pages: practical decisions
Use ConvertUrl when
- The page is publicly reachable or your converter can authenticate to it.
- Stylesheets, images, and scripts should resolve exactly as they do from the published page.
- You want SelectPdf to load the document as a browser-like navigation.
Use ConvertHtmlString when
- The server owns the markup and you want to avoid publishing an intermediate URL.
- You need to inject per-request data into a template.
- You can provide a stable base URL or absolute asset URLs.
For either path, make sure the conversion process can reach every required resource. Relative paths, blocked outbound traffic, login redirects, client-side rendering, and missing fonts are common causes of apparently “empty” PDFs.
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SelectPdf’s Community Edition page describes a free product for personal and commercial use, with no watermark and a limit of five pages per generated PDF. That edition is distinct from the commercial library’s trial, which the vendor describes as exposing full features while watermarking every page. The commercial library removes those limits under its license. Confirm the current page limit and licensing terms on the vendor’s pages before shipping or purchasing.
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The self-hosted library is also distinct from SelectPdf’s hosted REST API. Decide whether your requirements favor a library running in your Windows application or an online service, and review current terms directly with SelectPdf.
Reliability and production checklist
- Dispose deterministically: save first, then call
Close(), including in error-handling paths. - Use unique output names: avoid concurrent requests overwriting the same file.
- Control concurrency: conversion is resource-intensive; queue jobs or cap parallel work according to observed memory and CPU usage.
- Set operational timeouts: protect the web request from pages that never finish loading, while allowing enough time for legitimate assets.
- Test deployment parity: verify native engine files, fonts, write permissions, and outbound access on the production Windows host.
- Review sensitive data: PDFs may contain personal or financial information; secure temporary files and response headers.
- Check every output: examine page breaks, clipped content, missing glyphs, image resolution, links, and script-generated sections.
Troubleshooting common failures
“The type or namespace name SelectPdf could not be found”
The project does not reference the package, or the package targets a framework your project cannot use. Install the package matching your target framework, restore NuGet packages, and rebuild.
The application runs locally but fails on the server
Verify that the server is Windows when using the documented .NET Core package, that the correct engine companion package is deployed, and that the process can read engine files and write its output. Compare the runtime and package versions between environments.
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Relative paths need a base URL in ConvertHtmlString(html, baseUrl). Alternatively use absolute URLs or embed resources. Confirm that the conversion host can reach the asset URLs without an interactive login.
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JavaScript content is absent
The selected engine may not support the page’s JavaScript level, or the page may require asynchronous data after the initial load. Try the documented Blink or Chromium option where your target supports it, and simplify or server-render critical content. Validate the result in the deployment environment.
Only part of the document is produced
Check the Community Edition’s five-page limit and licensing mode first. If the limit is not involved, inspect CSS page-break rules, oversized elements, failed resources, and conversion timeouts.
Fonts or symbols are wrong
Install the required fonts on the conversion host or use a font available there. Missing fonts can change line wrapping and pagination even when the HTML appears correct in a developer browser.
Or skip the browser setup
If your requirement is a clean capture of a live page rather than a SelectPdf-generated document, ScreenshotNeo provides a website screenshot API and MCP server. A single request can return PNG, JPEG, WebP, or PDF. Its cleanup step accepts cookie or consent banners and removes more than 60 known consent platforms, newsletter popups, and chat widgets before capture; bot checks, blank pages, timeouts, failed loads, and cache hits are not billed, and response headers identify the page verdict and billing result. AI agents can use its MCP tools take_screenshot, get_page_info, and capture_pdf.
See the ScreenshotNeo documentation for all options. The basic cURL call is:
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Equivalent calls in Python and Node.js
These examples call ScreenshotNeo’s endpoint directly when an image or PDF capture is more appropriate than running a local HTML renderer.
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import requests
r = requests.get(
"https://api.screenshotneo.com/v1/shot",
params={"access_key": "YOUR_API_KEY", "url": "https://stripe.com"},
timeout=90,
)
r.raise_for_status()
open("shot.webp", "wb").write(r.content)Node.js
const q = new URLSearchParams({ access_key: 'YOUR_API_KEY', url: 'https://stripe.com' });
const res = await fetch(`https://api.screenshotneo.com/v1/shot?${q}`);
if (!res.ok) throw new Error(`HTTP ${res.status}`);
const fs = await import('node:fs/promises');
await fs.writeFile('shot.webp', Buffer.from(await res.arrayBuffer()));Frequently Asked Questions
Does SelectPdf work on Linux or macOS?
The current vendor guidance for the modern .NET Core package is Windows-specific and says it does not run on Linux or macOS. Verify support for the exact package and version you plan to deploy.
What is the difference between ConvertUrl and ConvertHtmlString?
ConvertUrl loads a page from an HTTP or HTTPS address. ConvertHtmlString renders markup held by your application; pass a base URL when that markup contains relative assets.
Why must I close PdfDocument?
SelectPdf’s API reference requires closing the document after saving to release conversion resources.
The Bottom Line
Install the package that matches your .NET framework and Windows deployment, use ConvertUrl for pages and ConvertHtmlString plus a base URL for generated markup, save the PdfDocument, and close it every time. Validate engine behavior, licensing limits, and output fidelity on the host that will run in production.
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