Difference Between PDF and Word: Which Format to Use

Neither format is better overall. They solve different problems, and most documents spend time in both, drafted in Word and sent as a PDF.

A .docx file is Microsoft Word's default format. It is a zipped bundle of XML files, defined by the Office Open XML standard, published as ECMA-376 and ISO/IEC 29500. It stores the text, styles, tables, images and comments as flowing content, not as finished pages.

Pages are worked out each time the file is opened. Word lays out the text using the fonts, page settings and Word version on that device. That is why the same file can break lines or pages differently on a colleague's computer, or look different in Google Docs, LibreOffice or Pages.

PDF stands for Portable Document Format. Adobe launched it in 1993, and it has been an open ISO standard, ISO 32000, since 2008. A PDF stores finished pages. Each character, line and image sits at an exact position, and the fonts are normally embedded, so the page is drawn the same way everywhere.

The cost of that stability is editing. Inside a PDF, text is stored as lines placed on the page, not as paragraphs that flow. Changing a sentence can mean the rest of the paragraph no longer fits. PDF editors handle small fixes, but for larger rewrites you convert the file back to Word.

The two formats sit at opposite ends of the same trade-off. Word gives up a fixed layout so the text can be edited freely. PDF gives up easy editing so the layout can't move.

File size depends mostly on images, not the format. A text-only .docx is usually small because it is compressed. Saving it as a PDF gives a file of similar size, sometimes larger, because the PDF carries the fonts it uses. With many photos, both formats grow, and a PDF can be shrunk further with a compression tool.

Both formats can be locked with a password. Desktop Word can encrypt a document with a password, though Microsoft notes that Word for the web can't. A PDF can have an open password with AES-256 encryption, plus permission settings that ask viewers to block printing or copying. Mainstream readers honor those permissions, but they are easy to remove, so treat the open password as the protection that counts.

Both formats support certificate-based digital signatures. Word adds them in the Windows desktop app and makes a signed file read-only. PDF is the usual choice for signed contracts, because its signatures follow the PAdES standard, readers report any change made after signing, and the signed page can't reflow. A signature image placed on the page is an electronic signature, not a digital one.

A Word document works with screen readers when you use real heading styles, lists and alt text on images. A PDF works with them only if it is tagged. Tags tell a screen reader what is a heading, a list or a table, and in what order to read. Scanned PDFs have no text at all until OCR adds it.

The easiest route to an accessible PDF is to fix the Word file first, then export. Microsoft recommends running Word's Accessibility Checker before you save as PDF. On Windows, keep the 'Document structure tags for accessibility' option ticked. On a Mac, choose 'Best for electronic distribution and accessibility'. Your headings and alt text then become PDF tags. The ISO standard for accessible PDFs is PDF/UA.

The rule of thumb is simple. If someone needs to change it, send Word. If someone needs to read, print, sign or keep it, send a PDF. When a recipient asks for a specific format, use theirs.

Word's own export gives the closest match, because it uses the same layout engine that drew the document. Without Word, PDFToolz Word to PDF converts a .docx in your browser without uploading it and keeps headings, fonts, lists, tables, pictures, headers, footers and page numbers. It doesn't open legacy .doc files.

Going the other way is harder, because a PDF has no flowing paragraphs to give back. Every converter has to rebuild them from lines placed on a page. Text-heavy documents such as letters, reports and contracts convert well. Complex layouts need checking.

PDFToolz PDF to Word joins wrapped lines into paragraphs, keeps bold, italic and font sizes, turns large titles into Word headings and places images near where they sat. Each PDF page starts a new Word page, with the paper size taken from the PDF. Tables come out as lines of text rather than Word tables, and the original fonts and exact positions are not kept. The conversion runs in your browser.