Doconut.app opens 70+ extensions in the browser, free and without an account, and deletes your file when you close the tab. It is a viewer: it does not store, convert or edit anything.
Here are the formats people arrive with most often, what the size ceiling is for each, and the one thing worth knowing about each before you conclude a file is broken.
1. PDF — up to 25 MB
The PDF viewer renders pages with the fonts and images the sender exported, and you can zoom, jump to a page and search the text.
Search is the thing to know about: it works on the text layer the file already carries. A PDF exported from Word has one; a scanned page does not, because its words are pixels. There is no OCR here, so a search that finds nothing in a scan is telling you about the file, not about the viewer.
2. Word — up to 15 MB
DOC, DOCX, ODT and RTF, plus the template variants .dot, .dotx, .dotm and .ott, in the Word viewer.
Expect the page breaks to land somewhere else than the author saw. Word stores font names, not fonts, so a typeface the rendering machine lacks is measured against a substitute, lines rewrap, and four pages become five. Nothing broke — the pagination was never stored in the file.
3. Excel — up to 20 MB
XLS, XLSX, CSV and ODS, plus the macro and binary variants, in the Excel viewer.
The important caveat: a viewer does not recalculate. Every formula cell holds the formula and the result Excel worked out at its last save, and what renders is the second one. If the workbook was left on manual calculation, or written by a script that could not evaluate formulas, the numbers on screen may be stale or blank. They are the file's numbers, faithfully shown.
4. PowerPoint — up to 20 MB
PPT, PPTX and ODP, plus the slideshow, macro and template variants, in the PowerPoint viewer.
You get one still image per slide, which explains the usual surprise: a slide built to reveal four bullets on four clicks stores four objects in the same place, so rendered as one frame they overlap. If one slide looks like a mess and the other thirty are fine, that is a build, not a damaged file. Speaker notes are a separate part of the file and do not appear.
5. Images — up to 25 MB
JPEG, PNG, GIF, BMP, WebP and AVIF in the image viewer. The awkward ones — SVG, TIFF, ICO, DNG, EPS, CDR, TGA, JP2 — are in the vector and raw viewer, which applies embedded ICC profiles and shows a photograph's EXIF beside the image.
And the rest
DWG, DXF and DGN drawings up to 10 MB in the CAD viewer, with layers you can switch off and distance and area measurement; PSD up to 25 MB; Visio, Project, EML and MSG email, EPUB and plain text each have a page of their own.
The pattern across all of them: the size ceiling belongs to the format, not to the site, and most of what looks like corruption is the format behaving normally in a tool that is not the one that wrote it.
Test it with your own awkward file at Doconut.app — the one that will not open. If you need it in a different format rather than just readable, that is OnlineDocumentViewer.com.