Converters: free online tools

5 free tools, processed locally in your browser.

Five moves from one format to another, with no technical common ground: a Word document to PDF, images to PDF, the audio track of a video to MP3, a CSV to an Excel workbook, Markdown to HTML. Each rests on a different library, and each loses something along the way. Knowing what avoids discovering the loss after the fact.

Two of these conversions have their mirror image elsewhere on the site: Word → PDF against PDF → Word, JPG → PDF against PDF → JPG. Those round trips are not reversible, since every pass rebuilds the document out of whatever survived the previous one.

Tools in the Converters category

Word → PDF: what gets rebuilt

Only .docx files are accepted; an old .doc is refused with a message inviting you to save it again in the current format. The mammoth library extracts the content of the document and turns it into HTML, which is then laid out in a column 794 pixels wide, photographed by html2canvas, and cut into A4 pages in the final PDF. Headings, lists, images and the flow of paragraphs are respected; columns and text boxes are flattened.

One consequence weighs more than the others: the PDF produced contains page images, not text. You cannot search it, and you cannot select a sentence in it. For a contract, a dissertation or anything meant to be quoted, the native PDF export in Word or LibreOffice remains preferable. This tool is for the case where that software is not available. Past two hundred rendered pages, the conversion stops.

Images to PDF, and audio to MP3

JPG → PDF also accepts PNG and WebP, and turns the order of the list into the order of the pages, adjustable with the arrows before you start. The page format is a choice between A4 portrait, A4 landscape and one fitted to each image: prefer A4 for receipts you intend to print, and the fitted mode for screenshots of varying proportions. Margins are zero, twenty-four or forty-eight points, and transparency is replaced by white.

MP4 → MP3 does not depend on a video converter but on the browser’s own audio decoder: the file is decoded to raw sound, then re-encoded to MP3 by lamejs at 96, 128 or 192 kbit/s. MP4, M4A, WebM, WAV and OGG containers go through most reliably; a file whose codec is not recognised triggers an error message listing the accepted formats. Duration is capped at forty-five minutes, and the interface suggests staying around thirty.

CSV → Excel: the separator trap

A CSV is a text file, and nothing in it makes the comma compulsory. French exports commonly use the semicolon, English-language spreadsheets the comma, and some tools the tab. The conversion analyses the first ten lines, counts those three candidates and keeps the most frequent one; the separator it settled on is displayed under the result, which lets you check that the file was read the way you expected.

The .xlsx workbook is written with SheetJS, column widths being estimated from the first two hundred rows so that cells are not truncated when the file opens. Those widths are clamped between eight and forty-eight characters, so a column holding long paragraphs stays readable instead of pushing the rest of the sheet off screen. The note under the download states the number of rows, the number of columns and the separator retained.

Two smaller details save time. Tab-separated .tsv files are accepted alongside .csv, and a UTF-8 byte order mark at the start of the file is stripped before parsing, so the first heading does not arrive with an invisible character glued to it. If the table nonetheless arrives as a single column, the detected separator was the wrong one.

Markdown → HTML and useful chains

The Markdown conversion relies on marked, with a preview rendered immediately and a cleaning pass over the HTML produced. Two outputs sit side by side, and the choice depends on the destination: the copied fragment drops into a CMS article or an existing template, while the downloaded HTML page is a complete file, with its stylesheet inlined, ready to open or to send as it is.

Chaining tools is often the right approach. Photos of documents are worth cropping and compressing before they are assembled into a PDF, otherwise the file you get is needlessly heavy. A PDF produced from a .docx can then go through the compressor to fit inside an attachment.

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