What happens to transparent backgrounds
Toolmera embeds the PNG as an image object in the PDF, including its alpha transparency data. On a normal blank PDF page there is nothing behind that image, so transparent areas usually appear as the page background, which PDF viewers commonly display as white.
The converter does not currently offer a PDF-page background color picker.
Why PNG works well for screenshots and diagrams
PNG is lossless, which makes it well suited to screenshots, UI mockups, diagrams and graphics with fine text or hard edges. Turning several of those images into one PDF creates a single file that is easier to attach, print, review or archive.
Each PNG becomes one PDF page and the output queue lets you arrange the page sequence before creating the document.
How Toolmera sizes PNG pages
Each PDF page is sized to the dimensions of the PNG placed on it. Images with different sizes or orientations can therefore produce PDF pages with different dimensions; A4, Letter, margin and padding controls are not currently included.