PDF generation and processing is a common requirement in many web applications, especially for generating invoices, reports, or documents dynamically. PHP provides various libraries to handle PDF creation, manipulation, and extraction. In this article, we will evaluate the most popular PHP libraries for PDF handling, breaking down their pros and cons, and advising when each library is best suited for specific use cases.

1. FPDF

FPDF is one of the most basic and lightweight libraries for creating PDF files with PHP. It requires no external dependencies and allows developers to generate PDFs from scratch using a simple API.

Pros:

• Lightweight: FPDF is minimalistic, making it easy to set up and use for basic PDF generation.
• Free: It's open-source and free to use, suitable for small projects.
• Simple API: The syntax is intuitive and easy for developers to understand, making it ideal for beginners.
• Customizability: Gives control over text placement, fonts, images, and shapes.

Cons:

• No HTML/CSS support: FPDF does not support converting HTML or CSS into PDF, making it harder to design complex layouts.
• Limited Features: While it's good for basic tasks, it lacks advanced features like embedding fonts, handling complex table layouts, and supporting Unicode.

Best Use Cases:

• Generating simple invoices, tickets, or certificates.
• Projects that don't require complex layouts or HTML-to-PDF conversion.

2. TCPDF

TCPDF is a robust, feature-rich library that builds on the simplicity of FPDF but provides more advanced capabilities like support for HTML, Unicode, and complex layouts.

Pros:

• Feature-Rich: TCPDF supports HTML and CSS, including tables, images, and complex document structures.
• Unicode Support: It has native support for UTF-8, making it ideal for multilingual projects.
• No Dependencies: Unlike other libraries that rely on external tools, TCPDF is standalone.
• Barcodes and QR codes: It has built-in support for generating barcodes and QR codes, a useful feature for product labels or tickets.

Cons:

• Performance: TCPDF is slower and more memory-intensive than FPDF due to its extensive features.
• Steep Learning Curve: Its vast array of features can be overwhelming for new users.
• Large Files: PDF files generated by TCPDF tend to be larger compared to those generated by FPDF or other libraries.

Best Use Cases:

• Applications that require multilingual or RTL text support.
• Generating complex documents with images, tables, and different fonts.
• Projects that need barcodes or QR codes within PDFs.

3. mPDF

mPDF is based on FPDF and HTML2PDF and is designed for converting HTML content into PDFs. It provides a good balance between simplicity and features, offering an easy way to convert web pages into PDFs.

Pros:

• HTML/CSS to PDF Conversion: mPDF excels at converting complex HTML structures (with CSS) into PDF, making it ideal for web-based PDFs.
• Unicode and RTL: It supports multilingual content, including right-to-left (RTL) scripts like Arabic.
• Embedded Fonts: Supports embedding custom fonts within the PDF, adding to design flexibility.
• Ease of Use: It’s relatively easy to convert a web page into a PDF with minimal configuration.

Cons:

• Performance: While fast for small documents, mPDF can become slow with large or complex HTML layouts.
• Memory Usage: mPDF consumes more memory than some other libraries when handling large documents.
• Limited Features: While it works well with HTML/CSS, it lacks advanced PDF manipulation features (e.g., extracting text from PDFs).

Best Use Cases:

• Converting web pages (HTML CSS) directly into PDF.
• Projects that require custom font embedding and support for multiple languages.
• Ideal for invoices, reports, or forms that are originally designed as web pages.

4. Snappy (wkhtmltopdf)

Snappy is a wrapper for the wkhtmltopdf command-line tool that uses WebKit to render HTML as PDF. It’s known for producing high-quality, accurate PDFs from complex HTML/CSS structures.

Pros:

• High-Quality Output: Snappy (wkhtmltopdf) delivers precise and accurate rendering of complex layouts, including advanced CSS and JavaScript.
• JavaScript Support: It can execute JavaScript, making it possible to include dynamic content (e.g., charts) in your PDF.
• Speed: wkhtmltopdf is relatively fast compared to libraries like TCPDF and mPDF for large documents.
• Command-line Utility: Allows for batch processing via the command line for server-side applications.

Cons:

• Requires External Tool: It depends on the wkhtmltopdf tool, which must be installed on the server.
• Limited PDF Manipulation: Snappy is great for converting HTML to PDF, but lacks advanced features like merging or splitting PDFs.
• Resource-Heavy: It can be resource-intensive, especially when generating PDFs from very complex HTML layouts.

Best Use Cases:

• Projects that need pixel-perfect HTML-to-PDF conversion.
• Applications where you need to convert large reports or invoices from HTML to PDF quickly.
• Dynamic web content (with JavaScript) that needs to be rendered as a PDF.

5. PDFParser

PDFParser is a powerful library for parsing and extracting content from existing PDF files. It focuses on analyzing and extracting text, images, and metadata rather than creating new PDFs.

Pros:

• Text Extraction: It efficiently extracts text, images, and metadata from existing PDFs.
• Search and Indexing: Useful for indexing and searching large collections of PDFs.
• Built on TCPDF: Leverages TCPDF’s capabilities for more complex parsing tasks.

Cons:

• No PDF Creation: PDFParser is specifically for extracting content, not creating or manipulating PDFs.
• Complex Documents: While it works well with simple documents, it can struggle with highly complex or encrypted PDFs.

Best Use Cases:

• Projects that involve PDF document indexing, searching, or text extraction.
• PDF content analysis or metadata extraction tasks.

6. SetaPDF

SetaPDF is a commercial-grade PHP library for professional-level PDF processing. It offers features like form filling, signing, and advanced manipulation of PDF files.

Pros:

• Enterprise Features: Includes professional-level features like digital signatures, form filling, and annotations.
• High Performance: Optimized for enterprise environments with high-volume PDF processing.
• Security: Offers advanced encryption and security features for PDF files.
• Rich API: Comprehensive API for advanced PDF manipulation.

Cons:

• Commercial License: SetaPDF is a paid library, which might be a barrier for smaller projects or individual developers.
• Complexity: The advanced feature set requires a steep learning curve and in-depth understanding of PDFs.

Best Use Cases:

• Enterprise applications that need secure, high-performance PDF generation, filling, or signing.
• Projects involving sensitive documents like contracts, legal papers, or certifications.

7. FPDI

FPDI is an extension to FPDF and TCPDF that allows you to import pages from existing PDFs and use them in newly generated PDFs. It's perfect for modifying and merging PDFs.

Pros:

• PDF Importing: Allows you to import, reuse, and manipulate existing PDF pages.
• Works with FPDF and TCPDF: Combines well with either library to provide enhanced functionality.
• Simple to Use: If you're already using FPDF or TCPDF, FPDI is easy to integrate.

Cons:

• No PDF Creation: FPDI is designed for manipulating and merging PDFs, not for creating new ones from scratch.
• Limited Editing: It’s great for importing and merging but limited for complex editing of PDF content.

Best Use Cases:

• Applications where merging multiple PDFs is required (e.g., combining invoices or reports).
• Projects that need to modify existing PDFs, like adding a cover page or watermark.

8. PDFMerger

PDFMerger is a small, easy-to-use library for merging PDF files. It simplifies the process of combining multiple PDF files into one document.

Pros:

• Simplicity: Very easy to use for merging PDFs.
• Quick Integration: You can quickly add this library to an existing project.
• Lightweight: Minimal dependencies and configuration needed.

Cons:

• Limited Functionality: Focuses purely on merging; does not support any other PDF manipulation.
• No Editing: You can merge PDFs but cannot modify their contents.

Best Use Cases:

• Projects that require merging multiple PDFs into a single file.
• Use cases like bundling invoices, contracts, or reports.

9. Dompdf

Dompdf is one of the most popular PHP libraries for converting HTML and CSS to PDF. It’s a powerful library that uses a layout engine based on HTML5 and CSS3, allowing developers to generate PDFs from existing web pages or dynamically built HTML documents.

Pros:

• HTML/CSS Support: Dompdf supports most HTML5 tags and CSS3 styles, making it suitable for converting complex web pages into PDFs.
• Ease of Use: Very straightforward for developers familiar with HTML and CSS, as it allows you to render PDFs directly from existing templates.
• Open Source: Dompdf is open-source and free, with a large community for support.
• Font Embedding: Allows you to embed custom fonts within the PDF for more design flexibility.
• Basic JavaScript Support: Supports basic JavaScript but is somewhat limited compared to other libraries like Snappy (wkhtmltopdf).

Cons:

• Performance: Dompdf can be slow when dealing with large or complex HTML documents, especially those with many images or heavy CSS.
• Limited Advanced Features: Compared to libraries like TCPDF or mPDF, Dompdf lacks advanced features like encryption, digital signatures, or form fields.
• Inconsistent CSS Rendering: While it supports CSS3, it can struggle with some advanced CSS properties, especially for responsive design elements.
• Memory-Intensive: Processing large PDFs can lead to high memory usage and longer generation times.

Best Use Cases:

• Web-to-PDF Conversion: Perfect for converting web pages into PDF, such as online invoices, reports, or newsletters that are built in HTML.
• Small to Medium-Sized Projects: Works well for web applications that generate medium-sized PDFs (e.g., e-commerce invoices, user manuals).
• PDFs with Custom Designs: Ideal for generating PDFs with custom fonts, layouts, and styling, particularly if the source content is already styled with HTML/CSS.

When to Use Dompdf:

• HTML-to-PDF Conversion: Like mPDF, Dompdf is designed specifically for converting HTML and CSS to PDF, making it the go-to choice for web applications that need to render dynamic HTML pages into PDF format.
• Simple Projects with Moderate HTML: It's ideal for medium-complexity documents that require basic to moderate HTML/CSS rendering. However, if your project involves large documents, high resolution images, or complex layouts, you may run into performance bottlenecks.
• Projects with Embedded Fonts: Dompdf’s ability to embed custom fonts makes it a good choice for documents where typography is essential, such as branded reports or certificates.

In summary, Dompdf is a great option for converting existing HTML content into PDF format when you have a simple or moderately complex design and don’t need advanced PDF features like encryption or form processing. However, for larger documents or projects that require more sophisticated PDF capabilities, you may want to consider alternatives like TCPDF, mPDF, or Snappy.

When to Use Each Library

• FPDF: Use when you need a lightweight solution for creating basic PDF documents from scratch.
• TCPDF: Ideal for generating complex, feature-rich PDFs with support for HTML, Unicode, and custom fonts.
• mPDF: Best for converting web pages (HTML CSS) into PDFs. Great for forms, invoices, and reports designed for the web.
• Snappy (wkhtmltopdf): Go-to for pixel-perfect conversion of complex HTML/CSS to PDFs, especially for reports or invoices.
• PDFParser: Suitable for extracting text and metadata from existing PDF files.
• SetaPDF: The choice for enterprise-level projects requiring secure PDF handling, digital signatures, and form processing.
• FPDI: Use when you need to import or manipulate existing PDFs within new PDF files.
• PDFMerger: Perfect for merging multiple PDFs into one document, ideal for report bundling.
• Dompdf: For converting HTML/CSS to PDF in small to medium-sized projects with simple to moderate layouts. It's ideal for web applications needing dynamic PDFs with custom fonts and designs.

Each library has its strengths and weaknesses, and the choice depends heavily on the specific requirements of your project. For HTML-to-PDF conversion, mPDF or Snappy are excellent choices. If you're dealing with secure enterprise documents, SetaPDF is your best bet. For basic tasks, FPDF offers a straightforward and lightweight solution.