Ctrl + D in acrobat pro, in security, choose password security

in Permission, check restrict editing and printing (none for both print and change, uncheck enable copying, optional disable enable text access, then put a password)

save as

in watermark tool, add a placeholder 0% watermark on top of all page,

in acrobat tool panel, add “Print Production” button, and click open,

right panel, click “Flattener Preview”, check Convert all text to outlines, all strokes to outlines (w bottom “all pages in documents”)

there is no way to set exact size, but if you Edit> Add image, your image size will be in ratio of your current image size,

if you zoom in pdf, when you place image, the image will be bigger in ratio

so you can make sure all your image is in proportion in image pixel size

then zoom in pdf at right level, add image in, so they will be all at certain size with same scale ratio

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if above not work well, you can try copy 1 image, and paste to another place, then replace that image, it will maintain same size