PDF and DOCX often hold the same words, yet they behave like two different objects. A DOCX file is a document that is still being written: text flows, pages rearrange themselves, and anyone with Word or a compatible editor can change it. A PDF is closer to a printed sheet: the pages are already laid out, and the file's job is to look the same wherever it is opened. Most problems people run into, such as a CV that arrives with broken formatting or a contract someone edited without asking, come from sending the wrong one of the two at the wrong moment.
This guide compares the two formats on what matters day to day, gives a decision guide based on real situations, and looks honestly at what survives conversion.
Quick answer
Use DOCX while the document is still changing: drafting, reviewing with comments and tracked changes, or when the recipient is expected to edit it. Use PDF when the content is final and must look the same for everyone: CVs, signed contracts, invoices, official submissions and archives. In practice, keep the DOCX as your editable source and send a PDF exported from it.
The core difference: fixed pages vs flowing text
A DOCX file (the Word format since 2007, based on the Office Open XML standard) is a zipped package of XML files. It stores paragraphs, styles, tables, comments and revisions, but it does not store finished pages. Page breaks, line endings and where a table splits are calculated every time the file is opened, by whichever program opens it, using whichever fonts that computer has.
A PDF stores the result of that calculation. Each page has a fixed size, every character and image has an exact position, and fonts are usually embedded. The reader only draws what is already described.
Everything else follows from this: DOCX is easy to edit because nothing is fixed, and PDF is reliable to share because everything is. Read more about what a PDF contains internally in What is a PDF file?
Editing and collaboration
In a DOCX, adding a sentence on page 2 pushes everything below it down and re-wraps the lines, which is exactly what you want while writing. Word processors also offer tools for working with others:
- Track changes: every insertion and deletion is recorded with the reviewer's name, and the author accepts or rejects each one.
- Comments attached to a specific word or paragraph.
- Styles such as Heading 1 or Body Text, so changing the look of every heading is one edit, not fifty.
- Automatic tables of contents, footnotes and cross-references.
Editing a PDF is a different kind of work. Because text is stored as positioned lines rather than paragraphs, a PDF editor changing a sentence has to squeeze the new words into the space of the old line. A typo or a date can be fixed well in a good desktop PDF editor; rewriting a paragraph usually ends with text overflowing or overlapping the next line, because nothing reflows.
PDF does support commenting: highlights and sticky notes are annotations layered on top of the page. That is useful for reviewing a final draft, but the notes still have to be typed back into the source document by hand. Page-level jobs, such as reordering, merging or removing pages, are a different story: they work well on PDFs because they treat each page as a whole unit.
Layout fidelity across devices and fonts
The most common complaint about sending a DOCX is "it looked fine on my computer". Here is why it happens. If you wrote your document in a font the recipient does not have, their program substitutes another one. Different fonts have different letter widths, so lines break in different places, a one-page CV spills onto a second page, and a table that fitted the margin now gets cut. The same file can also differ slightly between Word, LibreOffice, Google Docs and a phone preview.
Arabic and mixed Arabic/English text makes this more visible. Modern Word handles right-to-left paragraphs and letter shaping well; some mobile viewers and older editors are less consistent. A PDF exported from a program that handled the Arabic correctly keeps the result as you saw it, because the shaped glyphs and their positions are already in the file.
PDF fidelity has its own limits worth knowing:
- If a font was not embedded when the PDF was created, the reader substitutes one, and the look can change.
- A PDF does not adapt to small screens. An A4 page on a phone means zooming and scrolling sideways, whereas a DOCX opened in a mobile editor can reflow to the screen width.
File size
There is no rule that one format is always smaller. For a text-only document, both are compact, typically a few dozen to a few hundred kilobytes. A DOCX is already zip-compressed, while a PDF embeds its fonts (often only the characters used), which is why a short PDF can be bigger than its DOCX.
Images dominate size in both formats; what matters is how they were saved and at what resolution. A PDF made from scanned pages is the heaviest case, because every page is a full image: a single scanned page is often somewhere between 200 KB and 1 MB, depending on resolution and colour.
If a PDF is too big for an email or a portal, Compress PDF offers two modes. "Lossless" rewrites the file structure and keeps the text selectable, but the gain is usually small. "Strong" redraws every page as a JPEG image at the quality you choose; it shrinks scans and photo-heavy files a lot, but the text stops being selectable or searchable, so it is a poor fit for a CV or a text document. The tool shows the size before and after and never gives you a file larger than the original.
Security and permissions, and their limits
Both formats can be password-protected, and both have two very different kinds of "protection" that people confuse.
PDF: open password vs permissions password
An open password (sometimes called the user password) encrypts the file's content. Without the password, the pages cannot be displayed. With a long password and modern encryption, this is real protection; a short or guessable password is not, because cracking tools can try millions of guesses offline.
A permissions password (owner password) lets anyone open the file but asks reader programs to block printing, copying text or editing. This relies on the reader respecting the flags. Mainstream readers do, but many tools simply ignore them. Treat them as a polite request, not a lock. And whatever the settings, anyone who can see a page can photograph or screenshot it.
SmokePDF's Protect PDF adds an open password, so the file cannot be viewed without it; it requires at least 4 characters, but for anything sensitive use a long passphrase. Unlock PDF needs the correct password, or no password if the file only carries permission restrictions. The unlocked copy keeps its text, fonts and images as they were, so the text stays selectable and searchable.
DOCX: encryption vs restrict editing
Word's "Encrypt with password" genuinely encrypts the file; the same password advice applies. "Restrict editing" and "Mark as final" are deterrents only: they stop accidental changes, not a determined person.
Hidden content
A DOCX can carry things you did not mean to send: unaccepted tracked changes, deleted text still in the revisions, comments, and the author's name. Exporting a clean PDF of the final version avoids most of this. PDFs also carry metadata (author, creating software, dates), which you can inspect with the PDF Info tool. One more trap: drawing a black box over text in a PDF hides it visually, but the text is usually still in the file and can be copied out. Real redaction needs a tool that removes the underlying content.
Printing, archiving and accessibility
Printing
Print shops ask for PDF because what they print matches what you approved, with no font substitution or shifted page breaks. Printing a DOCX from your own computer usually works; sending one to someone else to print is where things go wrong.
Archiving
For long-term storage, a variant called PDF/A exists specifically for archiving. It forbids features that depend on the outside world, such as fonts that are not embedded, external content or encryption, so the file stays readable decades later. Word and LibreOffice can both export PDF/A, and some government and court systems require it. Archive both: the PDF as the record of what was sent or signed, the DOCX as the editable source.
Accessibility
Screen readers need structure: which text is a heading, the reading order, table headers, and alternative text for images. A DOCX built with real heading styles carries that structure naturally. A PDF can carry it too, as a "tagged PDF", but only if it was exported with tagging enabled; the "Save as PDF" option in Word does this when accessibility tags are turned on. A PDF made of scans or page images has no text or structure, so a blind user effectively cannot read it. If accessibility matters for your audience, export a tagged PDF from a well-structured source, or share the DOCX alongside it.
Which one to use: a decision guide
| Criterion | DOCX | |
|---|---|---|
| Purpose | Writing and revising | Sharing a finished version |
| Editing | Easy, text reflows | Limited to small fixes |
| Layout on other devices | Can shift with fonts and software | Stays the same if fonts are embedded |
| Collaboration | Track changes, comments, styles | Annotations on top of the page |
| Reading on a phone | Reflows in mobile editors | Fixed page, needs zooming |
| Password protection | Real encryption available | Real encryption (open password); permissions are weak |
| Printing and archiving | Depends on the printer's setup | Predictable; PDF/A for archives |
| Accessibility | Good with heading styles | Good only if tagged |
Use DOCX when…
- Collaborative drafting: a team is writing a report or policy together. Share the DOCX (or a shared online editor), use track changes, and export a PDF only once the content is approved.
- The recipient must edit it: a template, a form a colleague will complete in Word, or a contract the other party's lawyer wants to mark up.
- A recruiter or agency explicitly asks for Word: some applicant tracking systems or recruitment agencies want DOCX so they can parse it or add their own header. Follow the instruction.
Use PDF when…
- CV submission: unless Word is requested, send a PDF. Your one-page layout stays one page, your font is preserved, and nobody accidentally edits it. Export it from your word processor so the text stays selectable; many application systems read the text from the file.
- Contract for signature: once terms are agreed, send the PDF. Both parties then see the same pages and page numbers, and the signed version is fixed. Note that adding a signature image with Sign PDF is a visual signature, like a scanned handwritten one. It is not a certificate-based digital signature that proves the file has not changed since signing.
- Government forms and portals: administrations usually require PDF, often with a size limit. Fill the official form, save it as PDF, check the size, and keep a copy of exactly what you submitted.
- Invoices, certificates and archives: records should not change.
Converting between them: what survives and what doesn't
DOCX to PDF
This direction is straightforward if you use the program the document was written in. "Save as PDF" or "Export" in Word, LibreOffice or Google Docs lays out the pages exactly as that program displays them, keeps text selectable and searchable, keeps images, tables, headers, links and, if enabled, accessibility tags. For a CV, a contract or anything with careful formatting, this is the method to use.
SmokePDF's Word to PDF lays out the document's pages in your browser the way you designed them: page size and margins, headings, bold and italic, tables, images, lists, and right-to-left Arabic. It then gives you two options: a direct download in which pages are stored as images (layout kept, text not selectable), or "Save with selectable text" through the print window, where you choose "Save as PDF" and get real text. Page headers, footers and page numbers are not carried over, and fonts not installed on your device are replaced with a similar one. For complex documents, exporting from Word remains the most faithful route.
PDF to DOCX
Going back is always an approximation, because the PDF no longer knows where paragraphs, columns and tables were; it only knows where lines were drawn. Every converter has to guess the structure. Results are good on single-column text and worse with columns, complex tables, text boxes and forms.
SmokePDF's PDF to Word reads the existing text layer page by page, groups text pieces into lines by their vertical position, and writes each line as a paragraph in a real .docx file, with a page break between pages and Arabic lines set right-to-left. A short first line on a page is marked as a heading. What you get is the text, in order, ready to edit. What you lose: images, tables (cell contents become lines of text), columns, original fonts, colours and spacing. Because each original line becomes its own paragraph, you will usually need to join lines back into paragraphs before editing seriously.
A scanned PDF contains pictures of text, not text, so this tool will return nothing useful and will tell you the file looks scanned. That needs OCR (text recognition) first, which SmokePDF does not offer; our OCR guide explains the options.
The lesson: always keep the original DOCX. Converting a PDF back to Word is a rescue operation, not a workflow.
Frequently asked questions
Is DOC the same as DOCX?
No. DOC is the older binary Word format used before 2007; DOCX replaced it with a zipped XML package that is smaller and better supported by other programs. Modern Word opens both, but if you have a choice, save as DOCX.
Can someone change my PDF after I send it?
Yes, with a PDF editor anyone can alter text or swap pages, and permission restrictions will not reliably stop them. What a PDF gives you is a clear reference: keep your own copy of what you sent, and for contracts where tampering matters, use a certificate-based digital signature service.
Why does my DOCX look different on my phone?
Mobile apps often lack your fonts and support fewer layout features, so they re-flow the text with substitutes. The content is intact; only the rendering differs. If the look matters, send a PDF.
Should I send both formats?
Sometimes: a PDF so everyone sees the intended layout, and a DOCX for whoever needs to edit or reuse the text. Label them clearly so nobody reviews one while editing the other.
Can I fill in a PDF form without converting it to Word?
If the PDF has interactive form fields, most PDF readers let you type into them directly and save. If it is a flat or scanned form, printing it, filling it by hand and scanning it back is often more reliable than converting it to Word, which tends to break the form's alignment.
The bottom line
DOCX is for documents that are still changing; PDF is for documents that are finished. Draft and review in DOCX, export a PDF from the original program when the content is final, and keep both. Treat PDF permission passwords as a courtesy rather than protection, use an open password when confidentiality matters, and expect any PDF-to-Word conversion to give you the text, not the original design.
