Start from what you want to do. Each answer says what to expect, including where a tool stops.
Passport Photo Maker: getting a photo that passes
The tool handles the cropping and layout; the photo itself is up to you, and that is where most rejections come from. Stand about a meter from a plain, light wall, face the camera straight on with a neutral expression, and light your face evenly from the front so there are no shadows behind you. Take the picture from a little further away than feels natural, at eye level, so the head and shoulders fit with room to spare.
Choose the size, then the number of copies (up to 20), and download the PDF. Print it at actual size, 100%, not "fit to page", or the photos will come out slightly too small. The tool makes the 2×2 in (51×51 mm) US size, a 1×1 in stamp size and print sizes from 3R to 8R; it does not make 35×45 mm yet and does not change the background, so check your passport office’s rules before you print.
Remove Background: what makes a clean cut-out
The model looks for the main subject, so give it one: a person, a product or a pet, with some contrast against what is behind it. A coffee cup on a plain backdrop and a simple logo came out perfectly in our tests, in under 2 seconds; a portrait took 3.3 seconds and kept a small patch of background in one corner.
Zoom to 100% before you use the result. Soft edges around hair and fur are deliberate, so the cut-out blends onto a new background, but they can carry a faint halo of the old color onto a very different one. Busy scenes, glass and things touching the subject are where it has to guess.
Compress PDF: when it helps and when it cannot
Compress PDF never lowers quality: it stores the same content more efficiently. So the saving depends on the file. Reports and letters typed on a computer shrink most (26% for our 10-page test document); a PDF of scanned pages or photos may not shrink at all, and the tool says so instead of giving you an identical copy.
If an upload form has a size limit your scan cannot meet, the pictures themselves have to get smaller. The PDF Tools page walks through how to rebuild a scanned PDF from lighter images, which works for scans up to 50 MB; for bigger ones, scan again at 150 dpi in grayscale.
Edit PDF: signing and filling in forms
To sign, choose the draw tool and sign with your mouse, trackpad or finger; on a phone, turning it sideways gives you more room. Text boxes can go anywhere, with your choice of font, size and color, which is how you fill in a form that was never made fillable. Everything happens in the browser tab, so a contract or an application never leaves your device.
Two things to know: your text sits on top of the page rather than inside the form’s own fields, and a drawn signature is a picture, not a certified digital signature. For most forms you print, email or upload, that is exactly what is needed.