Dropping a logo onto an invoice, a headshot onto a CV, or a scanned signature onto a contract are all the same operation underneath: placing an image on top of an existing page. It is straightforward, it is free, and the difference between a result that looks professional and one that looks pasted on comes down almost entirely to how you prepare the image beforehand.
Prepare the image first
Most bad results are decided before the PDF is even opened.
Choose the right format. PNG supports transparency, which is what you want for a logo or a signature — the page shows through the background instead of a white rectangle sitting on your document. JPEG has no transparency and will always place an opaque block. Use PNG unless you are placing a photograph.
Remove the background. A signature scanned on white paper arrives as black marks on a white rectangle. Dropped onto a form, that rectangle covers the printed line underneath it. Removing the background so only the strokes remain is the single biggest improvement you can make. Free tools do this well, and most phone photo editors now have a one-tap background remover.
Get the resolution right. For print, aim for roughly 300 pixels per inch at final size — a logo appearing two inches wide wants about 600 pixels across. For screen-only documents, 150 DPI is plenty. Going much higher just inflates the file; a 4000-pixel logo on a business letter is wasted bytes.
Crop tightly. Whitespace around the image becomes whitespace you then have to compensate for when positioning. Crop to the content.
Get a clean signature capture. Sign a blank white sheet with a black pen — not blue, and not a fine ballpoint, which scans faintly. Photograph it in even daylight without shadows, crop tightly, increase the contrast so the strokes are properly black, and remove the background. Ten minutes doing this once gives you a signature image you will reuse for years.
Adding the image
In Docento.app, images are placed through the signature tool's upload option, which accepts any image file rather than only signatures:
- Open your PDF in the editor — the file is read by your own machine, with no upload to any server.
- Select the signature tool and choose upload.
- Pick your PNG or JPEG.
- Click on the page where the image should sit.
- Drag to reposition, and use the corner handles to resize. Resize from a corner rather than an edge so the proportions stay correct — a stretched logo is immediately noticeable.
- Export the finished PDF.
The tool is named for signatures because that is its most common use, but it places any image. For a logo or a small graphic this is all you need.
Other options if you want them: macOS Preview places images through its markup toolbar and is already installed. LibreOffice Draw opens PDFs and handles image insertion with more layout control. Acrobat and PDF-XChange Editor offer full image tools including layering and precise positioning.
Placing it well
Do not stretch it. Always resize from a corner. Distorted logos look careless in a way that reflects on the whole document.
Respect the margins. An image butting against the page edge risks being clipped when printed. Most printers cannot print to the very edge of the paper.
Line it up with something. Align a logo to the left margin of the body text or centre it properly on the page. An image sitting slightly off the text block reads as an accident.
Size a signature to its line. A signature overflowing the box and covering the printed terms looks worse than no signature. Zoom in and fit it to the space.
Check the contrast. A dark logo on a dark background, or a light one on white, disappears. Look at the exported result rather than the editor preview.
Common problems
The image has a white box around it. Your file is a JPEG, or a PNG saved without transparency. Convert to PNG and remove the background.
The image looks blurry when printed. Resolution too low. A 100-pixel-wide logo scaled up to two inches will be soft no matter what you do — go back to the original artwork.
The PDF became enormous. A high-resolution photo can multiply file size. If the result is too big to email, compress it — image-heavy documents often shrink dramatically with no visible loss.
The image moved or vanished for the recipient. If it was stored as an annotation rather than merged into the page, some viewers render it differently. Flattening on export makes it part of the page content. See how to flatten a PDF.
The image sits on top of text you needed to read. Move it, or shrink it. There is no text-wrap in a PDF — anything you place is simply on top.
A note about signature images
An image of your signature is worth treating as sensitive. Anyone who receives a document containing it can extract it and apply it to something you never agreed to. Two habits: do not post documents carrying your signature publicly, and where a document allows it, prefer a typed or drawn signature made at the time over a stored image file.
See how to sign a PDF online for the wider picture, and the beginners guide to editing PDFs for the rest of the toolset.
