> ## Documentation Index
> Fetch the complete documentation index at: https://webviewer-docs.mupdf.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Troubleshooting

## How can MuPDF WebViewer load a large document no problem but have problems exporting it?

This is a common issue with PDF WASM viewers, and it happens due to fundamental differences between how viewing and [exporting](/api-reference/document#export) work:

### Why Viewing Works Fine

**Streaming & Chunked Loading:**

* WASM PDF viewers (like MuPDF WebViewer) can request byte ranges for document pages on-demand
* They only render visible pages, keeping most content in compressed form
* Memory usage stays relatively low since only decoded page data is in RAM

**Optimized Rendering:**

* Pages are rendered on-demand as DOM elements
* Decoded images/fonts are cached but can be garbage collected
* The viewer works with compressed PDF streams directly

### Why Saving Fails

**Memory Explosion:**

* Saving often requires loading the entire PDF into memory at once
* All pages, images, fonts, and metadata must be accessible simultaneously
* WASM has limited memory (usually 4GB max, often much less)
* Large PDFs can easily exceed available memory, especially if they contain many images as this data gets stored in vast base64 data representations

**Processing Overhead:**

* Saving may involve recompressing or restructuring the PDF
* Form data, annotations, or modifications need to be merged
* Cross-reference tables must be rebuilt
* This creates additional memory pressure

### Browser-Specific Issues

**Chrome/Edge:**

* More generous with WASM memory
* Better garbage collection

**Firefox:**

* Stricter memory limits
* May need explicit memory management

**Safari:**

* Most restrictive with memory
* Often requires server-side processing

### Solution

**Update!**

<Info>
  As of WebViewer `0.10.0` we have since resoved this issue by implementing a more efficient exporting mechanism that works within the memory constraints of browsers. If you are still experiencing issues please ensure you are using **the latest version of MuPDF WebViewer**!
</Info>