# STL Viewer vs PDF Merger

The clearest difference is in-app purchases: STL Viewer at none against PDF Merger's 3. PDF Merger's advantage is update cadence (every 9 months vs every 43 months). On price, ads, device support and iOS requirement there is nothing between them.

Both are free to download. PDF Merger sells 3 in-app purchases, starting at $1.99 per 7 days. STL Viewer asks for nothing beyond the download.

STL Viewer ships an update every 43 months, PDF Merger every 9 months. The most recent releases landed on October 8, 2026 and October 7, 2026 respectively.

## The numbers

| Metric | STL Viewer | PDF Merger |
| --- | --- | --- |
| Price | Free | Free |
| In-app purchases | **No** | Yes |
| Ads | No | No |
| Update frequency | Every 43 months | **Every 9 months** |
| Size | 4 MB | 2 MB |
| Requires iOS | 17.0 | 17.0 |
| Devices | iPhone, iPad | iPhone, iPad |
| Age rating | 4+ | 4+ |
| Developer | [Felipe Marques de Barros](https://appshunter.io/developer/1459294806) | [Ahmet Bostancklioglu](https://appshunter.io/developer/1780554362) |

## What reviewers say

### STL Viewer

[App page](https://appshunter.io/ios/app/stl-viewer/id6445801487)

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases:** none


### PDF Merger

[App page](https://appshunter.io/ios/app/pdf-merger-combine-and-split/id6738798786)

**Features:** macOS Compatibility

**In-app purchases (3)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Pro — Weekly | $1.99 | per 7 days |
| Pro — Yearly | $29.99 | per year |
| PDF Merger Lifetime | $59.99 | one-time |


## Frequently asked questions

### Is STL Viewer free?

STL Viewer is free to download, with no in-app purchases.

### Is PDF Merger free?

PDF Merger is free to download, with in-app purchases available.

### Do STL Viewer or PDF Merger have ads?

Neither STL Viewer nor PDF Merger shows ads.

### Which is updated more often, STL Viewer or PDF Merger?

STL Viewer ships an update every 43 months, and PDF Merger every 9 months. Most recently, STL Viewer was updated on October 8, 2026 and PDF Merger on October 7, 2026.

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*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*