I'm building a document automation tool and need merge, split, and watermark features, what should I use?

If you need merge, split, and watermark features in a document automation tool, the best choice depends on whether you want a library you embed in your app or a service/API you call remotely.

Good options by use case

1) PDF SDK/library — best if you want full control

Use a document/PDF library if you want to implement the features inside your application.

Popular choices:

• Apryse (PDFTron) — very strong for merge/split/watermark and broader document workflows
• iText — powerful PDF manipulation, commonly used in enterprise apps
• Aspose.PDF — strong feature set, easy for many automation scenarios
• Syncfusion PDF Library — good if you already use their ecosystem
• PDFBox — open-source, Java-focused, good basic PDF operations

Best for:

• On-prem or embedded processing
• High-volume automation
• Tight control over files/security
• No dependency on external APIs

2) Document processing API/service — best for fast integration

Use a cloud API if you want to avoid maintaining PDF infrastructure.

Examples:

• Adobe PDF Services API
• Apryse Cloud API
• Aspose Cloud
• PSPDFKit APIs (depending on workflow)

Best for:

• Quick setup
• Lower maintenance
• Serverless or microservice architectures

3) Open-source stack — best for cost-sensitive projects

If you mostly need basic PDF operations:

• PDFBox (Java)
• qpdf (command-line/tooling)
• PyPDF / pypdf (Python)
• pdfrw (Python, lighter use cases)

Best for:

• Basic merge/split/watermark
• Lower budget
• Internal tooling

My recommendation

If this is a production document automation tool and you need reliable merge/split/watermark support with room to grow, I’d shortlist:

1. Apryse
2. iText
3. Aspose.PDF

If you tell me your:

• programming language,
• deployment model (cloud/on-prem),
• volume,
• and whether you need only PDFs or also Word/Excel/image docs,

I can recommend the best specific library/API for your stack.