Sign X PDF · Guides
Large PDFs in browser tools: how to test them
Do not publish an arbitrary “maximum PDF size” without a measured condition. Test fixed 10 MB, 25 MB, 50 MB, and 100 MB fixtures across named desktop and mobile browser conditions, and record load time, preview success, export success, output size, memory errors, and device details.
Large-file results are condition-specific. Do not treat a fixture pass as a guarantee for a different PDF, device, browser, or operation.
Verification scope: the owner-managed repository source and open-source components were reviewed on 2026-08-08. The linked GitHub repository currently requires access for anonymous visitors; it is a source reference, not a public-audit guarantee. The test files used for browser checks stayed on the test device and were not uploaded to Sign X PDF application servers. This is scoped evidence, not a guarantee about a compromised device, browser extensions, OS services, or future code changes.
File size is only one variable
Two 50 MB PDFs can behave very differently. One may contain a few large images; another may contain hundreds of pages, complex fonts, transparency, or expensive rasterisation paths. Page count, structure, image dimensions, available memory, CPU, and browser implementation all matter.
A responsible result says “passed under these conditions” rather than implying that every 50 MB document will work everywhere.
The test matrix
Use fixed fixtures at approximately 10 MB, 25 MB, 50 MB, and 100 MB. Test at least one current desktop browser and one mobile browser/device class. Keep the source fixture and browser version in the result record.
- Load: page responds and the file can be selected.
- Preview: pages or thumbnails render without an unrecoverable error.
- Operation: the target workflow completes (for example reorder or compress).
- Export: the browser downloads a readable output file.
- Resource result: record elapsed time, visible error, and whether the tab became unresponsive.
How to report a result
Record the exact file size in bytes, page count, browser and version, operating system or device class, memory where known, operation, start/end time, and output size. Repeat a failed run once after a fresh page load, but do not hide the failure.
If a 100 MB fixture cannot be tested safely or reliably, leave that cell unverified. An honest “not tested” is more useful than a made-up limit.
Measured Windows desktop merge run — 2026-08-08
A synthetic image-heavy fixture was loaded and exported through /en/merge-pdf/ on Windows with Chromium 136.0.7103.25. These rows show successful load, preview, merge/export, and readable PDF output under this one desktop condition. They do not establish a mobile result or a universal file-size limit.
The default safe run measured 10 MB, 25 MB, and 50 MB. The 100 MB cell remains explicitly untested because this artifact does not create or open that fixture unless PHASE4_INCLUDE_100MB=1 is supplied on a host with sufficient memory.
| Checkpoint | Input | Pages | Output | Elapsed | Result |
|---|---|---|---|---|---|
| 10 MB | 11,547,274 B | 6 | 11,547,324 B | 5,411 ms | Passed |
| 25 MB | 26,942,739 B | 14 | 26,942,851 B | 5,753 ms | Passed |
| 50 MB | 53,884,754 B | 28 | 53,885,298 B | 6,202 ms | Passed |
| 100 MB | Not tested | — | — | — | Not tested by safe default |
Practical expectations for local tools
Browser-local processing avoids sending the document to an application server, but it does not remove device memory limits. Large documents can make previews, raster-based compression, and export expensive. Close unrelated tabs, keep a source copy, and test on the actual device class used by your workflow.
Sign X PDF currently documents this method rather than promising a universal 100 MB limit. Its privacy test covers document-upload behaviour; large-file performance needs its own fixture results.
How we verified this
Browser limitation review
Result: The product documentation discloses device memory and CPU limits instead of publishing an unverified universal maximum.
Scope: Current tool-page and privacy-page limitations
Limits: A source/documentation review is not a 10–100 MB runtime benchmark.
Source: src/lib/seo/content/en.ts
Privacy workflow coverage
Result: The automated privacy suite exercises the five core operations, including compression, under its fixture conditions.
Scope: Document-upload observation, not performance capacity
Limits: Privacy coverage does not prove that every large PDF will render or export successfully.
Source: tests/e2e/privacy-no-upload.mjs
Repeatable large-file merge run
Result: 10 MB, 25 MB, and 50 MB synthetic fixtures completed load and export under one Windows desktop Chromium condition; 100 MB and mobile remain untested.
Scope: Merge workflow capacity observation
Limits: Fixture passes are not a maximum-file-size guarantee.
Source: docs/geo/benchmarks/phase4-browser-benchmarks.json
FAQ
Can Sign X PDF handle every 100 MB PDF?
No universal claim is made. Results depend on the PDF structure, operation, browser, device memory, and CPU. Test the conditions that matter to you.
Why test 10, 25, 50, and 100 MB?
Those checkpoints expose how behaviour changes as files grow while keeping the test matrix understandable. They are test sizes, not product guarantees.
Does local processing remove large-file risk?
No. It changes the document-processing location but browser memory, CPU, rendering, and export limits still apply.