Everything You Need to Know About the PDF

Learn what a PDF file is, how the format works, common uses, security features, and why it remains the most reliable way to share documents.

PDF is one of the most searched document terms on the internet. Most people use PDFs daily, yet many still ask a simple question: what exactly is a PDF file?

This guide explains the format in clear terms, covers why it matters, and shows where PDFs fit in with modern workflows across different platforms.

• What is a PDF file
• Why is the PDF file format widely used
• How does a PDF file work
• Types of PDFs and what they are used for
• How to work with PDFs in Xodo PDF Studio
• Frequently asked questions

What is a PDF file?

A PDF file is a digital document format that keeps text, images, and layout consistent on any device. The name stands for Portable Document Format. It was created so users could share documents without the design changing, regardless if they opened the file on Windows, macOS, Linux, a browser, or a phone.

A PDF acts like a fixed snapshot of a document, which is why it works reliably across different apps and platforms. The PDF preserves a document’s layout, fonts, images, and structure so it looks the same on every device.

Why is the PDF file format widely used?

PDFs are part of almost every industry workflow. Here are a few reasons the PDF format is commonly used:

1) Accuracy

A PDF keeps the same layout as the original document on every on every OS or device, retaining its formatting for printing, signing or archiving.

2) Standardization

PDF is an open ISO standard, making it attractive for government, legal, and corporate use.

3) Security

The PDF supports features that make the format suitable for legal, medical, financial, and enterprise use. A PDF can include:

• Password protection for opening the file.
• Permissions that limit printing, copying, or editing.
• 128‑bit or 256‑bit encryption for the file contents.
• Digital signatures for approvals.
• Redaction that permanently removes sensitive data.

4) Offline accessibility

Once a PDF is saved, you can open and read it without an internet connection, which is essential for business travel and confidential information.

5) Cross-platform compatibility

PDFs are used across all platforms and systems, letting teams work with and edit the same PDFs on different devices. They can keep the same workflow. No matter which system they’re on.

6) Widespread adoption

PDFs are created and shared each year in almost every industry, making it a default file format for sharing documents.

How does a PDF file work?

A PDF file stores text, images, vector graphics, form fields, annotations, and document structure in a self‑contained package.

Internally, it uses an object‑based model, which defines where each element appears on the page. Fonts are embedded or subsetted, images are stored as objects, and layout coordinates are fixed rather than reflowing.

That structure allows the PDF file to preserve layout and visual quality across different platforms, PDF editors and devices. PDFs may include:

• Vector shapes and lines
• Raster images
• Tags for accessibility
• Form fields
• Encryption keys
• Layers
• Metadata (title, author, keywords)

Simple PDFs, though, may contain only text and basic formatting, while complex PDFs (engineering drawings, research reports) may include layers or high-resolution graphics.

Common types of PDFs

Knowing the difference between PDF files can help with editing, converting, or scanning. There are different kinds of PDFs you should be aware of:

• Digital PDFs: Created in apps like Word, Excel, design tools, or code where its text is selectable.
• Scanned or image PDFs: Created from scanned paper documents. These PDFs require OCR to make them searchable.
• Interactive form PDFs: Contains fillable form fields for text, checkboxes, dates, and signatures for collecting data.
• PDF/A: An archival version of the PDF format. There are different types of PDF/A that follow strict rules to keep files readable long term.
• Secured PDFs: Locked by password, permissions, or digital signatures, secured PDFs can easily safe guard sensitive data.

What are PDFs used for?

PDFs play a role in almost every electronic digital document workflow. The most common industry uses include:

• Contracts and agreements
• Invoices and receipts
• Reports and presentations
• Government and tax forms
• Legal files and case bundles
• HR onboarding packs and policy manuals
• Engineering diagrams and CAD exports
• Research papers and academic reports
• Scanned archives and legacy records

If a file needs to be shared, printed, or archived without losing its layout, PDF is usually the format of choice.

How to work with PDF documents in Xodo PDF Studio

To open and work with PDF files with Xodo PDF Studio, follow these steps:

1. Download and install Xodo PDF Studio for Windows, macOS, or Linux.
2. Launch the app.
3. Go to the File tab.
4. Choose and open the document from your device.
5. Use any of the PDF tools on your document.
6. Once done, save the PDF to your computer.

You can perform different PDF tasks with Xodo PDF Studio's advanced PDF features:

• Edit text and content (Document tab): Edit your text formatting and adjust content.
• Annotate (Comment tab): Add annotations, comments, highlights, notes, shapes, or stamps.
• Fill or create forms (Forms tab): Add fields and signature fields, or fill existing fields.
• Extract data (Convert tab): Convert PDF files to Word, Excel, image, and other formats.
• Secure the file (Secure tab): Add a password, restrict permissions, or apply encryption.
• Batch process PDF (Batch tab): Secure, convert, archive, sign, and optimize multiple PDFs.
• Modify pages (Document tab): Insert, delete, crop and rotate pages or add watermarks and links.

Because Xodo PDF Studio is a desktop PDF editor, all of these steps work without an internet connection, on Windows, macOS, and Linux.

Frequently asked questions

1. What does PDF stand for?

PDF stands for Portable Document Format. It’s a popular file format that preserves the layout, fonts, and formatting of a document so it looks the same on any device or operating system.

2. How secure is a PDF file?

In general, PDFs are secure files. This depends on the PDF security applied to it. For users handling sensitive business documents, the PDF can support encryption, passwords, and digital signatures.

3. Why can’t I edit a PDF?

The PDF file may be secured, scanned, or created without editable text layers. Try using OCR if the PDF is created from a scanned paper document.

4. Is PDF a universal format?

Yes. PDF is supported on nearly every device, platform, browser, and operating system. The only specialized software technology needed is a tool with PDF viewer capabilities.

5. Do PDFs expire?

No. PDF is an ISO standard designed for long-term use. PDF/A is commonly used for archival purposes.

6. Can I convert PDFs to other formats?

Yes. You can use online converter tools or PDF editor software like Xodo PDF Studio convert PDF to images, text, and other file types.

7. What is a PDF/A file?

A PDF/A file is a version of PDF meant for long‑term storage. It keeps essential elements inside the file, such as fonts and color data, so the document can be opened years later independent of external resources. Businesses often use PDF/A when they need records to stay readable over time.

8. What is a PDF/X file?

A PDF/X file is a print‑ready version of PDF used in design and publishing. It includes rules for color, images, and fonts to create a consistent and standardized file for print publishing.

9. Why should I save my file as PDF?

You should save your file as a PDF because it keeps the formatting stable across apps and devices. It prevents layout changes, and supports security options. PDFs are ideal as reliable final versions of your electronic documents.

10. Can I view a PDF file on my phone?

Yes. Phones running iOS or Android can open PDFs with apps like Xodo Mobile. You can read, search, and add simple notes from your device, making it easy to review PDF documents on the go.

Open, view, and edit PDFs on any platform

PDFs keep documents consistent across devices, which explains their long-lasting popularity. They support forms, annotations, encryption, and long-term archiving.

Try a PDF editor like Xodo PDF Studio to handle PDFs offline on Windows, macOS, and Linux.