How to choose a document viewer: what to check

Six questions worth asking before you upload a file

You have a file that will not open, and a browser tab offering to open it. Whether that is a good trade comes down to six questions, and none of them are the ones a features table answers. Below is each one, what a straight answer looks like, and — since it would be odd to write this and go quiet about our own — how the viewer on this site answers it.

1. Where does your file actually get processed?

There are two designs behind a web viewer and they are not interchangeable.

Some render entirely inside your browser. The file never leaves your machine, which is the strongest privacy answer there is. The cost is coverage: the formats that work this way are the ones a browser already half understands, and a DWG, a PSD or a Visio drawing is not among them.

The rest, this site included, upload the file to a server, render it there and send back pages you can read. That is what makes it possible to open a Photoshop document on a machine with no Photoshop on it. Said plainly: your file travels to a computer that is not yours.

Neither design is the wrong one. What matters is knowing which one you are handing your file to, and a viewer that never says is answering the question anyway.

2. What happens to the file afterwards?

Once a file has been uploaded, the retention rule is the whole story, so look for it before you look at anything else. "Secure" is not a retention rule. "Deleted when you close the viewer" is.

Here, your upload is stored under a random identifier while it renders and is deleted when the viewing session ends. There is no sign-up and no email address, so there is no account for files to accumulate in. That is also the edge of the promise: for the minutes it is open, your document sits on our server, and if that is unacceptable for a particular file, no wording of ours should talk you out of it.

3. Does it open your file, or your file's family?

"Supports Office documents" is not something you can act on. A .docx opens almost anywhere; .docm, .dotx, .odt and a plain 1997 .doc are four separate promises. The only useful form of this claim is a list of extensions, and a site that cannot show you one is letting a family name do work its software cannot.

This viewer accepts 70+ extensions across seventeen pages. The formats page groups the common ones by family; the page for your own format is the one that answers the question, because the extensions and the ceiling it shows are read from the same registry its upload box enforces. Two things about lists like these are worth borrowing as tests for any viewer.

The list and the upload box should come from the same source. They did not always here. The home page once carried its own hand-written copy and rejected eight extensions that the individual pages opened without complaint — .epub, .ico, .dng, .cdr, .cmx, .tga, .eps and .htm. Two lists maintained by hand will drift, and the one you can see is usually the optimistic one.

Accepting a file is not the same as rendering it. The same upload box used to take .mpt, a Project template, which nothing behind it could draw. A file accepted and then failed is worse than a file refused at the door.

There is a gap in the other direction too, and a list is only honest if it names what is missing: the rendering engine also handles DICOM medical images, .dcm and .ima. They are deliberately not here. That is a separately licensed component, and a free public upload box is not where it belongs.

4. What is the size limit for your format, not for the site?

A single advertised limit usually describes the most forgiving format on the site, which is rarely the one you arrived with.

There are five different ceilings here, and which applies depends on the page you are on:

• 25 MB — PDF, PSD, TIFF, Visio, EPUB and images
• 20 MB — Excel, PowerPoint and Project
• 15 MB — Word, and the RTF page
• 10 MB — CAD (.dwg, .dxf, .dgn) and email
• 5 MB — HTML, XML and plain text

They differ because the files differ. Five megabytes is roomy for an XML export and turns away an ordinary architectural drawing, so the drawing page does not use it.

Even here the answer has a wrinkle, and it is the kind of thing worth poking at anywhere. An RTF is accepted by three separate pages — Word, RTF and text — at 15 MB, 15 MB and 5 MB. Same file, same extension, three ceilings depending on the door you came through.

5. Where is that limit checked, and does the number match the page?

An upload that fails after a two-minute wait tells you the check happens at the far end. On this site the extension and the size are both checked in your browser before anything is sent, so a file over the ceiling comes straight back, with the ceiling in the message.

The number in that message and the number printed on the page have to be the same, which sounds too obvious to test until it is not. The CAD page here advertised 10 MB while the uploader enforced 5, because the page and the uploader read two different tables. A file the page called acceptable was refused by the box directly underneath it. Both now read from one registry, which is the same reason the home page can no longer refuse a file that a viewer page opens.

This is the quickest of the six to check on any site: find a file just over the stated limit and drop it in. In about ten seconds you learn where the check runs, whether the published number is the enforced one, and what the failure looks like.

6. What does it refuse to do?

The list of things a viewer will not do is more informative than the list it advertises, and it is nearly always shorter to write. For this one:

• No OCR, anywhere on the site. Search works on the text layer a document already carries. A scanned page is a photograph of words, so searching it finds nothing — not because the search is weak, but because there are no characters in the file to find.
• It is not an editor. You can read, page, zoom, search where there is text, and print. Nothing you do changes the file.
• It does not convert. Reading a DOCX here does not give you a PDF of it; converting is the job of the sibling site, onlinedocumentviewer.com.
• It will not open a password-protected file without the password. You supply it, and the viewer does not work it out for you.
• One file at a time. No batch, no folder, no queue.

Where to start

The six answers you want from any viewer are: where it renders, what it keeps, which extensions exactly, the limit for your format, where that limit is enforced, and what it refuses to do. Five of those you can check yourself in a couple of minutes. The sixth is retention, and that one you have to be told — which is why a site that states it plainly is worth more than one that describes itself as secure.

If the file in front of you is a PDF, the free PDF viewer is the page to start on: 25 MB, no account, deleted when you are done. If it is something else, start on the page for that kind of file — finding out early that your extension is not among the ones it takes is the most useful thing that page can tell you.