Document format
What is a .pdf file?
PDF (Portable Document Format) is a format for documents that must look the same everywhere. It fixes text, fonts, images and page layout, so a file prints and displays identically on any device.
That fixed layout is also its limit: a PDF is made for reading and printing, not for rewriting. To change the text you need the original or a dedicated editor.
fileclay opens and writes PDF
PDF vs DOCX vs EPUB
| DOCX | EPUB | ||
|---|---|---|---|
| Layout | Fixed | Flows with editing | Adapts to the screen |
| Editing | Difficult | Easy | Difficult |
| Reading on a phone | Zoom needed | Needs an app | Comfortable |
| Printing | Exact | May shift | Not intended |
| Best for | Final documents, forms | Drafts, collaboration | E-books |
When to use PDF
Good for
- Contracts, invoices and forms
- Documents that must print exactly
- Sending a final version nobody should change by accident
Not a good fit
- Drafts that others will edit
- Reading long texts on a phone: EPUB adapts better
- Data you need to reuse in a spreadsheet
How to open .pdf files
| Platform | App | Notes |
|---|---|---|
| Any browser | Chrome, Safari, Firefox, Edge | Built in |
| Windows | Edge, Adobe Acrobat Reader | Edge is built in |
| macOS | Preview | Built in |
| iPhone, iPad | Files, Books | Built in |
| Android | Google Drive, Files | Built in |
| Editors | Adobe Acrobat, LibreOffice Draw | Edit with limits |
Convert PDF files
How to identify a .pdf file
Every PDF starts with the text “%PDF-” followed by its version, such as 1.7 or 2.0.
It’s read here, in your browser. Only the first bytes.
Your file
What comes after
Questions about PDF
Can I edit a PDF?
Only in a limited way. Text is placed on the page rather than flowing, so editors work around it. Converting to DOCX is often easier.
How can I reduce the size of a PDF?
Most of the size is usually images. Compressing them reduces it a lot, and fileclay can do it in your browser.
Is PDF a vector format?
It can be. Text and drawings are vector, while photos and scans are images inside the page.
What is PDF/A?
A version for long-term archiving. It embeds everything it needs and forbids what could stop working, such as external links to fonts.
Why does a PDF look different in another app?
Usually because a font wasn’t embedded. Fonts inside the file display the same everywhere.