PDF file: what it is and how to open it
A PDF is a document saved so every page looks the same on any screen or printer. Drop one here to read it now, or open it in the reader built into your browser or phone.
Drop your PDF file here
Opens on this device. Nothing is uploaded. Any other file works too.
What is a PDF file?
PDF (Portable Document Format) is how finished documents travel: contracts, invoices, boarding passes, manuals and forms. It records exactly where every letter, line and picture sits on each page, so the document looks the same on a phone, a laptop or paper. A PDF can also carry links, bookmarks, form fields, comments, attachments and digital signatures.
Adobe introduced PDF with Acrobat 1.0 on June 15, 1993 and published the specification so anyone could build readers and writers. In 2008 the format became an ISO standard (ISO 32000-1, PDF 1.7), and PDF 2.0 followed as ISO 32000-2; its current edition dates from December 2020. An ISO committee maintains it today, not a single company.
For documents that must stay readable for decades there is PDF/A (ISO 19005): fonts must be embedded and encryption is not allowed. A PDF/A file is still an ordinary PDF and opens in any reader.
What is inside
A PDF is a set of numbered objects: pages, fonts, images, form fields, annotations and metadata. Each page is a list of drawing instructions, and large parts such as images are usually compressed. Embedded fonts let the text display correctly on a device that does not have them installed.
The file ends with a cross-reference table that records where every object starts, so a reader can jump straight to page 300 without reading the first 299. Edits can be appended to the end without rewriting the original bytes, which is how a signed PDF can show what changed after signing.
%PDF-1.7header: the format and its version1 0 obj << /Type /Catalog >>the document’s starting point2 0 obj << /Type /Pages >>the page tree3 0 obj << /Type /Page >>one page and its drawing instructions4 0 obj << /Type /Font >>fonts, images, forms, comments…xrefwhere each numbered object startstrailer << /Root 1 0 R >>which object to read first%%EOFend of fileHow to open a PDF file
Windows
- Microsoft EdgeBuilt in and the default PDF reader on Windows 11. Reads, prints, fills forms and adds notes.
- Adobe Acrobat ReaderFree. Also opens dynamic XFA forms that browser viewers cannot show.
- Universal File Opener for WindowsOursFill forms, sign, annotate and read scans with offline OCR for free. Pro edits text, organizes pages and converts to Word, Excel or PowerPoint.
Mac
- PreviewBuilt in. Reads, annotates, fills and signs forms, reorders and combines pages.
- Adobe Acrobat ReaderFree. Use it for dynamic XFA forms.
iPhone and iPad
- FilesBuilt in. Tap the PDF to preview it.
- PreviewBuilt in from iOS 26. Fills and signs forms and scans paper to PDF.
Android
- Files by GoogleFree, and installed on some phones. Reads, searches, prints and marks up PDFs.
- Google DriveFree. Reads, fills in forms and annotates.
- Universal File OpenerOursRead, fill and sign offline for free, with OCR for scans in six languages. Pro edits text, redacts, organizes pages and converts to Word, Excel or PowerPoint.
In a browser
- Chrome, Edge or FirefoxEach has a built-in PDF viewer that reads, fills forms and adds simple marks.
- Universal File OpenerOursDrop the PDF on this page to read it and see what it carries: attachments, form data, signatures, JavaScript. Merge, split or compress a copy. Free, nothing uploaded.
Won’t open?
It asks for a password
The file is encrypted with an open password, and no reader can show it without that password. Ask the sender. A separate owner password only limits printing or copying; the file still opens.
A form shows only “Please wait…”
It is a dynamic XFA form, which browser and phone viewers cannot display. Download it and open it in Adobe Acrobat Reader on Windows or Mac.
The reader says the file is damaged
The download or attachment was probably cut short. A PDF keeps its index at the very end, so a truncated file cannot be read. Download it again and compare the file size.
A downloaded “PDF” opens in nothing
Drop it on this page: we detect the type from its bytes. A real PDF starts with %PDF-. If it turns out to be a web page or an error message, the site sent the wrong thing; download it again from the original page.
I cannot select or search the text
The pages are scanned pictures with no text layer. Chrome’s PDF viewer on a computer recognizes the text, and so does the OCR in our Android and Windows apps.
Convert a PDF file
- To WordOpen the PDF in Microsoft Word with File, Open. Word converts a copy and leaves the PDF unchanged; text documents convert best.
- To editable textIn Google Drive on a computer, right-click the PDF and choose Open with, then Google Docs.
- To PDFFrom any document on Windows, print to Microsoft Print to PDF. On a Mac, choose File, Print, then PDF, Save as PDF.
PDF files in our apps
Read, fill and sign PDFs offline on Android. UFO also edits supported text, marks up pages, reads scans with offline OCR in six languages, redacts content, organizes pages and converts PDFs to Word, Excel or PowerPoint. Text editing and rendering have limits, listed below.
All Android tools and limits for PDF files
- Fill & Sign: draw or type on the page, place a saved reusable signature, stamp APPROVED/DRAFT-style stamps, add sticky notes, highlight, underline, strike out, draw lines, arrows, boxes, and ovals.
- Forms: fill AcroForm text fields (including multiline), checkboxes, radio groups, and dropdown choices; read-only fields are labeled and kept inspection-only.
- Edit text: choose an editable paragraph to change its words, size or color. The app marks locked paragraphs and explains restrictions.
- OCR: recognize scanned pages in English, Spanish, French, German, Hindi or Indonesian for reading, search, copy, read aloud and text export, then save a searchable PDF copy. Both are free.
- Pages: rotate, delete, move, insert blank pages, extract a range, combine another PDF, split into separate files, and drag-reorder in a full-page thumbnail grid.
- Redaction: remove marked content by rasterizing affected pages. Those pages lose their original text and vector structure.
- Document finishing: page numbers, Bates IDs, headers, footers, watermarks, logical page labels, crop margins, compress images, flatten annotations.
- Protection: open password-protected PDFs (RC4, AES-128, AES-256) and save an AES-256 password-protected copy.
- Reading and inspection: search, outline/table of contents, night mode, a selectable extracted-text reading view with read-aloud, plus inspectors for links, layers, digital-signature metadata, form fields, embedded attachments and images, comments, and active content such as JavaScript or submit actions.
- Convert: PDF to Word saves editable paragraphs with pictures beside the text and ruled grids as Word tables; PDF to Excel saves a table you select as literal cells; PDF to PowerPoint saves one page picture per slide.
- Create PDFs from camera scans and from photos with Scan to PDF and Images to PDF.
- Export: extracted text as a .txt file, pages as JPG or PNG images, print through the system dialog, and save-all for attachments and embedded images.
- On tablets, the PDF editor uses the same ribbon as the Windows app.
- Free saves: form filling, signatures, highlights, notes, drawings, OCR text, searchable copies, scans and Images to PDF. Pro saves text edits, page changes, redaction, finishing, protection, and Word, Excel, PowerPoint or image conversions.
Limits
- Signature inspection reports signer metadata and byte-range coverage; it is not cryptographic certificate-chain validation.
- OCR models for all six languages ship inside the app; nothing is downloaded. PDFs with selectable text use their existing text layer.
- PDF to Excel converts one selected table at a time, and PDF to PowerPoint slides are page pictures, not editable text. A PDF that forbids content extraction cannot be converted.
- Text editing changes size and color, but not the typeface. Text stays within the paragraph and cannot reflow across pages.
- Malformed files and unsupported PDF structures can limit rendering or editing. The app reports the affected operation.
Walkthrough: Fill, sign and edit PDFs on Android