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Yes, you can use JavaScript in some PDF templates—but the right method depends on where the code is supposed to run. In PDFMonkey Code Templates, add a <script> block in the HTML tab; in its Builder, use the Custom JS editor or a script-enabled HTML block. Those approaches run code as part of preparing the template for PDF rendering. JavaScript embedded in a finished PDF is different: it runs only in a PDF viewer that supports the relevant PDF scripting features. Do not assume one service’s JavaScript behavior applies to another.
First decide which kind of PDF JavaScript you need
“JavaScript in a PDF template” can mean code that changes the HTML before it becomes a PDF, or code embedded in the resulting PDF for a compatible viewer to run later. A visual template builder may also provide its own scripting interface. These are different execution contexts, with different data access, restrictions and compatibility concerns.
| Approach | When the JavaScript runs | What it changes |
|---|---|---|
| HTML-to-PDF template script | During template rendering or the browser-based stage of PDF generation; exact behavior depends on the service. | The template’s HTML and rendered content before or during PDF creation. |
| Visual builder script | According to the builder’s own script controls and generation process. | Builder data, bindings, or a specific HTML block. |
| JavaScript embedded in a PDF | When a compatible PDF viewer opens or interacts with the finished file. | The PDF document through viewer-supported PDF APIs. |
Adobe’s Acrobat JavaScript developer documentation describes APIs for creating and modifying PDF documents. PDF-LIB’s PDFDocument API also documents adding JavaScript that executes when a PDF is opened. Neither fact means that ordinary browser JavaScript pasted into any PDF template will run in every viewer. If your goal is to calculate or format content before it is printed, use the template renderer’s supported scripting route. If the PDF itself must react after delivery, check the target viewers’ support and security settings.
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In PDFMonkey Code Templates, place the script in the template’s HTML tab. If the script needs to read the input data payload, enable JavaScript injection in the template settings first; the injected data is exposed as $docPayload. The following example assumes the payload has a customer_name field and the HTML includes an element with the matching ID:
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<div id="customer-name"></div>
<script>
document.getElementById("customer-name").textContent =
$docPayload.customer_name || "Customer";
</script>Use textContent for plain text rather than inserting untrusted input as HTML. Adapt the field name and fallback to your actual payload. The example is a template-rendering pattern, not code embedded in the final PDF.
Account for template processing order
PDFMonkey documents that Liquid interpolation runs before JavaScript. A Liquid expression therefore cannot read a value computed later by JavaScript. If Liquid can format or select the value you need, use Liquid in the template; reserve JavaScript for work that genuinely requires it. This avoids a common ordering mistake: expecting a server-side template expression to resolve a browser-side variable after the script runs.
External scripts are not always available
PDFMonkey’s Code Templates documentation says URL-loaded JavaScript requires a paid account and that documents using it fail on a free account. Check the account requirement and the script URL before building a template around a CDN library. A remote dependency also means generation relies on network access to that URL. If a small helper can be written inline, that reduces dependency and availability risks.
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PDFMonkey Builder offers three relevant places to put code: its template-wide Custom JS editor, scripts inside HTML blocks, and the External Assets manager for libraries. Choose the narrowest scope that fits the job.
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Use Custom JS for shared helpers
Put template-wide formatting or utility functions in the Custom JS editor. If a binding or another HTML block must call a function, attach it to window so it is available outside the local script scope:
window.formatCurrency = function (value) {
return new Intl.NumberFormat("en-US", {
style: "currency",
currency: "USD"
}).format(value);
};Then a binding or block can call window.formatCurrency(value). Change the locale and currency to match the document’s requirements; the example’s US formatting is not appropriate for every audience.
Use an HTML block for local behavior
For code that belongs to one part of the design, put the script in that HTML block and enable the relevant “Run scripts in editor” setting. If the block calls a shared helper, expose that helper on window as shown above. A function that exists only inside another script’s local scope may not be visible to the block.
Add libraries through External Assets when needed
Use Builder’s External Assets manager for third-party libraries, and confirm that the generation environment can reach the asset URL. PDFMonkey says Builder external assets require an internet connection at generation time. A library that loads on your development machine can still fail when a document is generated in an environment without access to its host.
Keep global scripts focused on modest formatting and utility work. PDFMonkey cautions that heavy computation or DOM manipulation can slow generation. Do substantial data preparation before sending the template input when practical, and avoid doing the same expensive work separately in multiple blocks.
How to make charts, dates and layout behave
Charts need print-oriented settings
For its Chart.js example, PDFMonkey recommends disabling animation and responsive sizing: PDF output does not play animations, and responsive sizing can lead to layout surprises. For example, use chart options along these lines:
options: {
animation: false,
responsive: false
}PDFMonkey describes Chart.js as its most reliable chart option; treat that as vendor guidance, not an independent comparison of chart libraries. Its documentation also notes that ApexCharts can show black borders in certain PDF readers, particularly Windows and Android readers. Inspect the generated file in the viewers and on the devices your recipients actually use.
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Handle time zones explicitly
A server’s time zone may differ from the time zone intended for display. PDFMonkey’s Code Templates documentation recommends Liquid time-zone and date filters for common formatting needs. If JavaScript is necessary, toLocaleString accepts a locale and options, including a time zone:
const displayTime = new Date(isoDate).toLocaleString("en-GB", {
timeZone: "Europe/London",
dateStyle: "medium",
timeStyle: "short"
});Supply an appropriate time-zone identifier and locale for the reader; do not rely on the server’s default zone when the displayed time has business or legal significance.
Check the renderer version for older templates
PDFMonkey’s documentation, updated September 20, 2026, says engine v5 is based on Chrome 133 and advises checking engine versions for older templates. Rendering behavior can change as the service updates its engine, so verify the current version and test templates whose output depends on browser-specific behavior.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why isn’t my JavaScript running when I generate a PDF?
Start by identifying the execution stage. A template service may substitute data without executing arbitrary JavaScript, may run code in a later browser stage, or may embed script for a PDF viewer. These stages are not interchangeable.
Do these 3 things before closing this tab:
1Fix the driver behind crashes, sound loss and screen glitches2Repair Windows errors before they cause bigger problems3Scan for outdated or missing drivers - takes under a minute| Symptom | Likely cause | What to check |
|---|---|---|
| Payload variable is undefined in a PDFMonkey Code Template | JavaScript injection is not enabled, or the payload field name differs. | Enable injection in template settings; inspect the actual payload and correct the field reference. |
| Liquid output ignores a value computed in JavaScript | Liquid runs before JavaScript. | Format or select the value with Liquid, or render it into the DOM with JavaScript instead. |
| Template fails after adding a remote script | The account may not support URL-loaded scripts, or the script URL may be unreachable. | For PDFMonkey Code Templates, confirm the paid-account requirement and verify URL availability; for Builder assets, confirm generation-time internet access. |
| A Builder block cannot call a helper | The helper is not exposed globally, or the block’s script setting is off. | Attach shared helpers to window and enable “Run scripts in editor” for the block. |
| Chart is blank, clipped or laid out unexpectedly | Animation, responsive sizing, loading, or reader-specific rendering may be involved. | Try the documented Chart.js settings, confirm the library loads, then inspect the PDF in target readers. |
| Dates differ by a few hours | Code is using a server or viewer default time zone. | Set an explicit time zone using Liquid filters or JavaScript locale options. |
| JavaScript in a PDF does nothing after opening | The selected viewer may not support the script or API, or scripting may be restricted. | Test in the intended PDF viewer and distinguish PDF-level JavaScript from template-time JavaScript. |
Debug the generated HTML, then the PDF
For PDFMonkey Code Templates, use the Debug button to open generated HTML in a browser and inspect errors in the console. This can reveal syntax errors, missing elements and failed script loads. Then inspect the final PDF too: a successful browser preview does not prove the PDF rendering stage or a recipient’s reader will behave identically.
What changes when the provider is not PDFMonkey?
Do not copy a PDFMonkey implementation into another service without checking that service’s documented execution model. PDF.co’s “PDF from HTML Template” documentation says arbitrary JavaScript is not executed during its template-substitution stage. It describes later headless-browser execution as possible, but not guaranteed in every environment. A script that appears in the template may therefore be ignored at substitution time or behave differently later.
Before choosing an implementation, establish these points in the provider’s documentation:
- Authoring model: HTML template, visual builder, or PDF-level scripting.
- Execution stage: data substitution, browser rendering, or PDF opening.
- Data access: how input fields are exposed and whether scripts can read them.
- Dependencies: plan restrictions, network access and library-loading behavior.
- Compatibility: renderer version and target PDF-reader support.
- Output purpose: whether code changes HTML before rendering or manipulates an already formed PDF.
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FAQ
Can JavaScript in a PDF template read the data I submit?
Only if that template system exposes the input to its script runtime. In PDFMonkey Code Templates, enable JavaScript injection to access the payload as $docPayload; other services may expose data differently or not run the script at that stage.
Will JavaScript in my generated PDF work in every PDF reader?
No universal compatibility is established here. Embedded PDF scripting depends on the viewer and its supported APIs and settings. Test the actual output in the readers your recipients use.
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Use Liquid when it can perform the required formatting, especially because Liquid interpolation precedes JavaScript execution. Use JavaScript for behavior or transformations that need the browser-side DOM or JavaScript APIs.
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