During last few days we're experiencing some delay in website stmp provider channel.
Some notification email from the website might not reaching containers.
We're working on a definitive solution.
for my application it is important to recognize each pdf i have worked with.
First: My idea was to add a custom meta field in the header like "/CustomID(123123)"
Unfortunately you only support getting the meta tags, it should be easy to implement a setterMethod for the meta tags.