How to fill out a PDF form without Adobe or uploading it
PDF forms come in two very different types. Knowing which one you have saves a lot of frustration.
Someone sends a PDF and says "fill this in." You open it, click where the first field should be, and nothing happens. You try a different spot. Still nothing. So you print the whole thing, fill it by hand, scan it again, and email it back feeling like this should have taken thirty seconds instead of ten minutes.
The reason it happened is that you had a flat PDF, not a real form.
Why clicking works on some PDFs and not others
A PDF with actual fillable fields was built that way on purpose. Whoever made it added form elements using software that supports AcroForm: text boxes, checkboxes, dropdowns. These are real objects inside the file. Click one and a text cursor appears. Tab to the next field and it jumps.
A flat PDF has none of that. It might look like a form, with printed blanks and labels everywhere, but it is really just a picture of a form. There are no field objects in the file. Clicking anywhere does nothing because there is nothing there to click. It might be a scan of a paper form, or a form that was designed but never had interactive fields added.
You do not need Acrobat for a real form
If the PDF has clickable fields, your browser can often fill it out. Open the file in Chrome or Firefox, click the fields, type. Most simple forms work fine that way.
For more control over how things look, a dedicated tool is better.PDFShore reads the field data already in the PDF, fills the form locally, and downloads the result as a new file. Nothing is uploaded.
What to do with a flat PDF
If clicking does nothing at all, use the Add Text tool instead. It lets you click anywhere on the page and type, which covers the printed-blank situation. The result looks a bit different from a neatly filled form, but it is readable and avoids the whole print-scan-email loop.
A few things that can cause problems
Some fields are set to read-only by whoever made the form. If a field accepts your input but the downloaded file still shows the original value, the field is probably locked and there is no workaround.
A PDF with an existing digital signature is locked too. Any change to a field would break the signature, making the whole document read-only. You would need the sender to remove the signature before you can fill it.