I’m working on a clunky PC that won’t allow me to install anything to fill in the PDF so was hoping I could use a site. What’s the best one to use?
I know you want an online one, though I don’t know of any to recommend. But have you tried a relatively lightweight (compared to Adobe) PDF reader program that allows annotation? PDF-Xchange Viewer is a pretty good free one that does annotation without putting watermarks on the file. Like with most free versions, just make sure that you choose “Custom Install” and don’t install any “extras” (like Toolbars or Search providers) the installer offers to add, sometimes by default.
I am not sure what you are asking. PDF forms, that you can fill in on the computer, are created, as special PDF files, to be fillable. You should not need a special application beyond your regular PDF viewer in order to fill it in. A web site can’t display a PDF for you unless you already have a PDF viewer (the “standard” one is Adobe Reader) installed on your computer. If you can read the form, but can’t fill it in, it is probably a regular PDF document that you are expected to print out and then fill in by hand (and maybe, then scan, if you are supposed to return it electronically).
There is a workaround for this, however. Get yourself a PDF reader that includes annotation tools, and use this to fill in the form. I recommend PDF XChange-Viewer, which can be downloaded for free here (see the box on the left for the free version, not the “Buy now” button - the EXE installer version is probably the easiest one to install), then use its Typewriter Tool to fill out the form. PDF-XChange has a lot of features that Adobe Reader does not, and is also less likely to act as a conduit for malware. [ETA: Blast, ninjaed on this bit by voltaire! (Shouldn’t he have died back in the 18th century?)]
If you can’t install anything, however, you are probably screwed.
I can’t install anything.
Hah, I ninja’ed you AND I included the link! 
But what you said made me think, if he’s having problems installing something for whatever reason, the best version to get is actually the “Portable ZIP | 8mb” version in the right-hand column of my link. That version doesn’t need to be installed in Windows, you just unzip the folder and it runs exclusively from within that folder without the need to install it at all. You could even download/unzip to and run it from a USB drive, or anywhere else.
Thank you, yes, that seems to be doing the trick. 
Can you read the PDF at all? And why can’t you install anything? Is this an IT dept policy thing, or what?
Here is the link I meant to include (probably the same as voltaire’s). As he said, the “portable ZIP” version might still work for you.
It took some team work, but glad to help!
Seems like the OP’s issue is resolved, but for any folks who need a PDF online form filler, I’ve been using PDFescape for a few years. Works fine, free.
I have a question about this. I don’t actually have (or want) the Adobe reader. Will this work even so. And I have a default reader (it is called Sumatrapdf) that must remain default. I want this only so I can fill out things like insurance forms consisting mostly of boilerplate occasionally. Will this pdfexchange do that?
[moderating]
Here’s a hint, folks: When your thread title begins with “What’s the best,” the post most likely belongs in IMHO rather than GQ. I have moved this one.
[/moderating]
Yeah, it’ll work fine, you don’t need Adobe and it’s okay if you have Sumatra installed as your default PDF program. Obviously if you double click a PDF to open it, it will open in your default (Sumatra), so you’ll either have to open PDFs within PDFXchange once it’s running, or else drag and drop the PDF files over to it.
Just be sure to get the same “Portable ZIP | 8mb” version mentioned upthread. It doesn’t get installed anywhere, you just run it from where ever you unzip that folder to. Where ever you choose to put that folder (My Documents, USB drive, etc.), you could even make a shortcut on your desktop to the program (the executable in that unzipped folder) that will launch it conveniently.