Printing something at its true size
The real size template list sets the box to an exact physical size rather than making you type it. The card sizes come from ISO/IEC 7810, the standard every national ID and bank card is built to: ID-1 is 85.60 × 53.98 mm and covers bank cards, EU driving licences and the current Romanian carte de identitate; ID-2 is 105 × 74 mm, the older Romanian buletin and other pre-2000s European cards; ID-3 is 125 × 88 mm, the passport booklet page. Photo sizes follow each country's published requirement — 35 × 45 mm across the Schengen area, the UK, India and Australia, 51 × 51 mm for the United States, and 50 × 70 mm for Canada, which is the only country that uses it.
Those fractional millimetres are not decoration. A card cut at 54 mm instead of 53.98 will not sit properly in a wallet slot or a badge holder, and the difference is invisible on screen — you find out at the print shop. Typing the number by hand is exactly where that error creeps in, which is the reason the list exists.
One thing has to be right at the printer, and it is not part of this tool. Print dialogs default to "Fit to page" or "Shrink oversized pages", which rescales the whole sheet by a percent or two to clear the printer's unprintable margin. That is enough to make a true-size card come out wrong. Set the scale to 100% or "Actual size" before printing, then measure the result with a ruler before cutting anything.
Because a template fixes the box to a real-world aspect ratio that will rarely match your photo, Keep image proportions crops the image to fill the box instead of stretching it. Leave it on for anything with a face or a logo in it; turning it off stretches the image to the box exactly, which is occasionally what you want for a texture or a background but never for a portrait.
Coordinates start at the bottom left
PDF's coordinate system has its origin at the bottom-left corner of the page, with y increasing upwards. Almost every other system you will have used — screen coordinates, CSS, canvas, image pixels — puts the origin at the top left with y increasing downwards.
This is the most common source of confusion when placing content, and it produces a very recognisable symptom: an image that should sit near the top of the page appears near the bottom, mirrored about the horizontal centre line. The fix is to subtract your intended top offset and the image height from the page height.
Positions are in points, 72 to the inch, so on A4 the top-left corner is (0, 842), and one inch in from the left and one inch down from the top is (72, 770). Working in those units directly avoids a conversion step and a rounding error.
Resolution, not display size, decides print quality
An image placed at two inches wide on the page prints at whatever its pixel count divided by two gives you. A 200-pixel-wide logo placed two inches wide is 100 ppi and will look visibly soft in print, no matter that it looked sharp on screen at its native size.
For print, aim for around 300 ppi at final placed size — so a two-inch-wide logo wants roughly 600 pixels. For screen-only documents, 150 ppi is generally sufficient. There is no benefit to going far beyond 300; you add bytes without adding visible detail.
Logos and diagrams are the case where format matters most. A raster logo is fixed at its pixel count, while a vector one stays sharp at any size and usually occupies fewer bytes. If a vector version of the artwork exists, use it — the difference on a printed page is obvious.
Transparency, colour and stacking
PNG transparency is supported, but it is carried in PDF as a separate soft mask object rather than as part of the image data. Some older or simpler PDF processors discard or mishandle that mask, which is why a transparent logo occasionally appears with a black or white box behind it in one particular reader while looking correct everywhere else.
If a document must render identically across unknown software, compositing the image onto a known background colour before placing it removes the risk entirely. It is less flexible and considerably more predictable.
Colour is the other cross-medium trap. Screen images are RGB and commercial printing is CMYK, and the conversion cannot reproduce every RGB colour — bright saturated blues, greens and oranges shift most noticeably. Placement order matters too: content added later is drawn on top, so an image placed after the text will cover it rather than sit behind it.