Documents
PDF (Portable Document Format) is a file format that preserves the exact layout, fonts and graphics of a document so it renders identically on any device.
Updated 12 Aug 2026
A document that looks the same everywhere
Word processors reflow text based on the fonts and settings of whichever machine opens the file. A PDF instead records the exact position of every glyph and graphic, and embeds the fonts it needs, so page 7 looks the same on a phone, a laptop and a printer a decade from now.
Text PDFs and scanned PDFs
A PDF exported from software contains real text objects: you can select, copy and search them. A scanned PDF contains only page images, so it looks identical but has no searchable content until OCR adds a text layer. Knowing which you have explains most PDF frustrations, from failed searches to enormous file sizes.
Security features
- A user password encrypts the file so it cannot be opened without it
- An owner password restricts printing, copying or editing while the file still opens
- Digital signatures prove authorship and detect later modification
- Redaction must remove the underlying content, not merely draw a black box over it
Because layout is fixed, PDFs resist tidy editing. Change the source document and re-export where you can; edit the PDF directly only for small corrections.
Merge PDF
Merge, split, compress, sign, protect and unlock documents in your browser.
Characteristics
- Fixed layout with embedded fonts and vector graphics
- Open ISO standard, readable by every platform
- Supports encryption, permissions and digital signatures
- May contain real text, page images, or both
Common uses
- Contracts, invoices and official forms
- Reports, brochures and print-ready artwork
- Long-term archiving with the PDF/A profile
- Scanned records and correspondence
Advantages
- Identical rendering on every device and printer
- Universally supported without special software
- Built-in protection, permissions and signing
- Stable for long-term archiving
Limitations
- Awkward to edit compared with a word processor
- Poor reflow on small screens
- Scanned PDFs are large and not searchable without OCR
- Accessibility depends on correct tagging, which many files lack
Examples
Try selecting a line of text.
Selectable -> text-based PDF (searchable, small)
Not selectable -> scanned image PDF (needs OCR, large)Frequently asked questions
What is a PDF used for?
Sharing documents whose layout must stay exactly as designed — contracts, invoices, reports and print artwork.
Why can't I edit my PDF easily?
The format stores positioned glyphs rather than flowing paragraphs, so text does not reflow when changed.
What is the difference between a scanned and a text PDF?
A text PDF holds real characters you can search; a scanned PDF holds page images until OCR is applied.
Are password-protected PDFs secure?
Modern AES encryption is strong, but permission-only passwords are trivially bypassed by many readers.
Why is my PDF so large?
Almost always embedded high-resolution images or full font files rather than the text itself.
Related terms
PDF Compression
PDF compression reduces the file size of a PDF by re-encoding its images, removing redundant objects and compressing content streams, ideally without visible loss of quality.
OCR
OCR (Optical Character Recognition) converts text inside images and scanned documents into real, selectable and searchable characters.
Image Compression
Image compression reduces the byte size of a picture by removing redundant or visually unimportant data, either losslessly or by discarding detail the eye barely notices.
JSON
JSON is a lightweight text-based data format commonly used to exchange structured data between applications and APIs.
XML
XML (Extensible Markup Language) is a text format that describes data using nested, self-labelled tags, designed for documents and long-lived system-to-system messaging.
CSV
CSV (Comma-Separated Values) is a plain-text table format where each line is a row and each field is separated by a delimiter, usually a comma.
Related tools
Related guides
How to Merge PDF Files Without Uploading Them
Combine several PDFs into one document: how merging works, how to control page order and orientation, what breaks bookmarks and forms, and how to do it without uploading files.
How to Compress a PDF Without Wrecking the Quality
Understand what actually makes a PDF large, which compression settings matter, how much size you can realistically save, and how to compress a PDF privately in your browser.
Compress PDF Without Losing Quality
Honest guide to shrinking a PDF without wrecking it: Lossless (small safe savings), Compress images (re-encode photos, keep text selectable), and Rasterize (biggest savings, flattens pages). Pick the mode that matches your file.
CSV vs JSON: Choosing the Right Data Format
Compare CSV and JSON on structure, nesting, file size, streaming, typing and tooling, with clear guidance on which to use for exports, APIs and analytics pipelines.