How to Fax a PDF Online and Choose Scan Settings

Begin with the recipient’s instructions. The office may specify a form version, the order of attachments or a dedicated fax number. Keep those instructions beside the draft so you can verify the packet against them before submitting.

• Gather the original PDF and any required attachments. Use the signed version when a signature is required.
• Enter the fax number and country code. Verify the destination against a trusted source from the recipient.
• Upload the files and arrange them in the requested order. Add a cover sheet when it helps the office route the packet.
• Open the final PDF. Check the first and last pages, then review every page for clipping, rotation, small text and missing annotations.
• Submit through an enabled delivery connection and keep the fax reference. Use the recorded status to decide whether to follow up with the recipient.

• Get a fillable fax cover sheet
• Fax from an iPhone or Android

An exported PDF can keep its text and lines as drawing instructions. A scan saves the page as a grid of pixels. Printing a digital PDF and scanning it again adds a rasterization step and can make small text harder to inspect.

The vector source for our four-page fixture was 6,708 bytes. Raster variants of the same pages ranged from 623,783 to 2,502,191 bytes. This source used standard PDF fonts, simple shapes and no photos. A PDF with embedded fonts, complex diagrams or photos will have a different baseline. The comparison shows the effect for this packet.

When the original contains fillable fields or annotations, open the version you plan to send and check what appears in print view. If an entry disappears in the final preview, export a copy that visibly includes it, then replace the file in the draft and review it again.

With grayscale and JPEG quality 85 held constant, our packet measured 0.82 MiB at 150 ppi, 1.22 MiB at 200 ppi and 2.04 MiB at 300 ppi. The 200 ppi output was about 40% smaller than the 300 ppi output. The 300 ppi file was about 2.5 times as large as the 150 ppi file.

Choose resolution by inspecting the page you need to send. For a clean typed letter, start at 200 ppi if the recipient gives you a choice. When the original has 7-point print, thin table lines or a faint stamp, try 300 ppi and check those details. Use the recipient’s required settings when provided. The benchmark measures size, so a smaller file alone tells you nothing about whether a particular field remains readable.

A U.S. Letter page measures 8.5 by 11 inches. At 150 ppi it is 1,275 by 1,650 pixels. At 200 ppi it is 1,700 by 2,200 pixels. At 300 ppi it is 2,550 by 3,300 pixels. Each value is per page. Doubling resolution in both directions gives four times the pixels before compression.

PDF bytes do not have to grow fourfold with the pixel count. The encoder can compress blank margins and repeated patterns. A dense page of fine text, a colored stamp and a noisy phone photo will compress differently. Resampling an existing low-resolution image upward adds pixels but cannot restore the details that the original scan missed.

At 300 ppi and JPEG quality 85, the grayscale PDF used 2.04 MiB and the color PDF used 2.39 MiB. Grayscale reduced the output by about 14% for this packet. Lowering grayscale quality from 85 to 65 reduced it again, from 2.04 MiB to 1.50 MiB, about 27% fewer bytes.

Use grayscale when tone carries the information and colors are incidental. Keep a color original if redlines, stamp colors or a legend are needed to understand it. Verify how the document will render for the receiving channel. For JPEG compression, check for smudged thin lines and faint gray characters after any change. Quality numbers describe one encoder’s settings and do not translate directly between scanning apps.

Read the destination and cover page first. Review the files in their final order and count the pages including the cover. Turn sideways scans upright, remove pages that were included by mistake and check that you can read fields near the edge of the page. If a file is cut off, re-export or rescan the original before trying stronger compression.

In Fax, the current upload workflow supports PDF and selected image and Office formats. It accepts up to 10 documents, 40 MB per document and 100 MB combined, with a 250-page limit on the assembled fax including any cover page. The receiving office can set its own limits. Allowance and delivery are separate from being able to upload a file.

If the packet is too large, first remove material the recipient did not request. Then check whether an original PDF can replace a raster copy. If you need to rescan, test the settings on the most difficult page and verify it in the final packet before you process the rest.

• See supported file types and upload limits
• Understand fax delivery confirmation

We built a synthetic cover sheet, application, itemized statement and supporting letter on U.S. Letter pages. The fixture used 7- to 10-point body text, form rules, numeric fields and a colored sample stamp. It contained no customer data. Poppler rendered the four pages at 150, 200 and 300 ppi.

For each resolution we encoded the page images in grayscale and color, at JPEG quality 65 and 85, with Sharp. The color output used 4:4:4 chroma sampling. Each variant was assembled with pdf-lib as a four-page PDF with one embedded JPEG per page. The resulting files were measured in bytes. The tables round MiB to two decimal places. The CSV records exact byte counts and raster dimensions for all 12 profiles and the vector original.

The test used one clean synthetic packet. It did not measure OCR accuracy, manual reading accuracy, time to upload, fax modem resolution or delivery success. A photograph of a folded or shadowed document may behave differently. The report uses file size as one input to a choice that still requires reviewing the actual pages.

• Download the 12-profile benchmark CSV