Adding images in a PDF or image file in C++

Hi :) I'm new on Stackoverflow.

Currently a lecturer gave a project that basically goes like this:

1) A clerk writes a letter in MS Word (an unsigned letter). This letter is then converted to a PDF (using Word's SAVE AS option);

2) Letter is input into a system, where an Approver reads it, and then approves it (if all conditions are met);

3) Upon approval, the Approver must append his/her signature at the signature line in the letter (the sign. is in some image format, maybe JPG or transparent PNG)

4) Letter goes back to clerk, who will now send it to the appropriate receiver(s). All done paperless-ly (an attachment in an email)

I'm imagining to develop this system using C++. But at the moment, have very little idea on how to be able to add the signature part. I'm with the idea that the letter will be in PDF format. So my question, is there anything in C++ that allows me to drag a signature (transparent PNG, but JPG is good enuff) onto a PDF file, and place it at a particular location? (in this case, the signature line at the bottom of the letter).

Maybe, besides a PDF, the letter can also be an image itself! So either PDF or an image file.

I've looked at online resources such as PHPWord, ImageMagick. But it seems nothing is fitting my needs. Any help would be greatly appreciated (just pointing me in the right direction... I will try my best to figure out the code)

Thank you!