I don’t want to use an app I want to implement this functionality with a short code.
Is there anyone willing to help?
Hi @Danielaaa 
Make sure you are being clear on what the goal actually is and your not self prescribing the wrong work.
there is no “shortcode” for such advanced functionality, there’s not even 1 single way to implement such things based on what you even mean by “link different Product Pages to the Color swatches”
In some themes if your not using the variant pick just disable or remove the block in the product template.
Then either use a custom-html/custom-liquid block and put in some HTML from an online button generator that are links but also style the buttons to be specific colors(swatches)
Or if you must try and DIY this with code see the .dev liquid docs on product and swatches and/or metafields to build a bespoke solution:
https://shopify.dev/docs/api/liquid/objects/product
If you need this advanced customization create for you then contact me for services
Contact info in forum signature.
ALWAYS please provide context, examples: store url, theme name, post url(s) , or any further detail in ALL correspondence.
If you want to implement this functionality without an app, you can add a simple code snippet to your Shopify theme that links your images to the uploaded PDFs in the Files section. If you need assistance with the specific code or placement, feel free to ask for help, and I can guide you through it!