By Alexey Spasskiy · Published February 10, 2025 · Updated February 10, 2025 · 6 min read
Quick Answer: You don't need a fax machine to send a PDF as a fax. Upload your PDF to mFax.to, enter the recipient's fax number, and hit Send — the service converts the PDF to fax format automatically and delivers it in minutes.
Converting a PDF to fax sounds technical, but it's actually one of the simplest things you can do with a document today. Every major online fax service — including mFax — accepts PDFs directly and handles the format conversion in the background. You never touch a fax machine, a printer, or a phone line.
This guide covers four methods for sending a PDF as a fax, from the fastest (mobile app) to options that work entirely from email or a web browser.
No Conversion Required
Modern fax services automatically convert your PDF to the TIFF Class F format that fax machines understand. Just upload the PDF and send — the technical conversion happens behind the scenes.
What Actually Happens When You "Convert" a PDF to Fax
When you send a PDF via an online fax service, the service converts your file to TIFF Class F — the standard image format used in internet faxing (defined in RFC 3949). Each page becomes a grayscale raster image at either 204×98 DPI (standard) or 204×196 DPI (fine), then the transmission goes out over the public switched telephone network (PSTN) as if it came from a traditional fax machine.
You don't need to trigger this conversion manually. The moment you upload a PDF and click Send, the service handles it automatically.
What this means practically:
- Color content prints in black and white on the recipient's machine
- Fonts, vector graphics, and images are all rasterized
- A 300 DPI scan in your PDF will render cleanly at fax resolution
- Very small text (under 8pt) may become hard to read
Method 1: mFax App — Fastest from Any Phone
The quickest way to convert a PDF to fax is the mFax app on iOS or Android. Upload from your files app, enter the fax number, and send — no computer needed.
Open the mFax App
Download mFax from the App Store or Google Play and sign in. If you don't have an account, sign up takes under a minute.
Tap 'Send Fax'
On the home screen, tap Send Fax and then Attach Document.
Select Your PDF
Choose your PDF from your phone's Files app, iCloud Drive, Google Drive, or Dropbox. mFax accepts PDFs up to 500 pages.
Enter the Fax Number
Type the recipient's fax number including the area code. For international faxes, include the country code (e.g., +44 for UK).
Send and Confirm
Tap Send. You'll receive a delivery confirmation — green means the fax was received, with a timestamp and page count.
From Google Drive or Dropbox
In the mFax app, you can attach PDFs directly from Google Drive and Dropbox without downloading them to your phone first.
Method 2: Email to Fax — No App Required
Every major fax service offers an email-to-fax gateway. You compose a normal email, attach your PDF, and send it to a special address. The service converts the PDF and transmits it as a fax automatically.
How the address format works:
Most services use this pattern: [fax-number]@[service-domain]
For example, if you use mFax and the recipient's fax number is (415) 555-0100, you'd send to: 14155550100@mfax.to
Open Your Email Client
Works with Gmail, Outlook, Apple Mail, Yahoo, or any email provider.
Compose a New Email
In the To field, enter the fax number in your service's email-to-fax format. The email body becomes your cover page message.
Attach the PDF
Attach your PDF as you would any normal email attachment. Most services support up to 20–100 MB.
Send
Hit Send. Within 1–3 minutes you'll receive an email confirmation with delivery status.
For a full walkthrough of this method with Gmail, see our guide to sending a fax from Gmail.
Method 3: Web Browser — Works on Any Device
No app, no email client — just a browser. This works on any computer, tablet, or phone.
Go to mFax.to
Open mFax.to in any browser. Log in or create a free account.
Click 'Send Fax'
From the dashboard, click the Send Fax button.
Upload Your PDF
Drag and drop your PDF into the upload area, or click to browse files. You can also link directly from Google Drive or Dropbox.
Enter Fax Number and Optional Cover Note
Type the recipient's number and an optional cover page message.
Preview and Send
mFax shows a preview of each page before sending — useful for catching formatting issues. Confirm and click Send Fax.
Method 4: From a Computer (Windows and Mac)
If you prefer a desktop workflow, you can send your PDF as a fax directly from Windows or macOS without any third-party app. See our full guide to faxing from your computer — it covers Windows Fax and Scan, Mac's built-in fax print dialog, and online alternatives that work without configuring a phone line.
For most users, the browser method above is simpler and doesn't require a modem or phone connection.
What File Formats Can Be Faxed?
PDF is the most reliable format for faxing, but most services accept several others:
| Format | Type | Notes |
|---|---|---|
| Document | Best choice — preserves layout exactly | |
| TIFF / TIFF Class F | Image | Native fax format, ideal for scans |
| DOCX / DOC | Document | Word files accepted by most services |
| JPG / PNG | Image | Good for single-page scanned documents |
| TXT / RTF | Text | Plain text transmits cleanly |
| XLS / XLSX | Spreadsheet | Supported by many services; complex formatting may shift |
Password-Protected PDFs Won't Send
If your PDF has a password or DRM restrictions, the fax service can't read it. Remove the password protection before uploading. Most PDF readers (Preview on Mac, Adobe Acrobat) have a "Save without password" option.
PDF Optimization Tips for Cleaner Faxes
Not all PDFs fax equally well. These adjustments take seconds and make a visible difference:
Convert to grayscale before sending Fax machines print in black and white regardless. A color PDF with red text or light yellow highlights may lose contrast. Export a grayscale version from your PDF app first.
Keep text at 10pt or larger Fax resolution is lower than print. Text below 8–10pt often becomes illegible after transmission, especially on fine-resolution mode.
Use standard page sizes Stick to US Letter (8.5"×11") or A4. Non-standard sizes may be cropped or scaled by the receiving machine.
Maintain 0.5" margins on all sides Content near the edge can be cut off by older fax machines that have narrower print areas than modern printers.
Compress large files first Very large PDFs take longer to transmit and occasionally cause transmission errors. Use the free mFax Optimize PDF tool to reduce file size without losing legibility.
Comparing the Four Methods
| Method | Best For | Requires App | Works on Mobile |
|---|---|---|---|
| mFax Mobile App | Fastest on-the-go sending | Yes (free) | Yes |
| Email to Fax | No new tools; works in existing email | No | Yes |
| Web Browser | Any device, quick access | No | Yes |
| Desktop Software | Regular heavy senders; Windows/Mac | Yes | No |
For most people sending occasional faxes, the mFax app or web browser method is the right choice. For high-volume business faxing, see our comparison of the best online fax services.
If you prefer faxing through email specifically, our guide to faxing from email covers every major provider's email-to-fax address format.
Send Your First PDF Fax Now
Converting a PDF to fax requires no technical steps on your end — just upload, enter a number, and send. The fax service handles the format conversion automatically.
Try mFax.to — upload your PDF, enter the recipient's fax number, and send. Works from any phone or browser. Delivery confirmation included.
For documents that aren't already in PDF format, use the free mFax Document Converter to convert Word files, images, or other formats to PDF before faxing.