Storing pdf files in archive

Which AWS service are you intending to use? When you say "AWS Archive" are you referring to S3 Glacier?

That would be straightforward enough, you should familiarise yourself with S3 lifecycle rules as well as the costs of Glacier retrieval, and also decide on the method you would use to deposit files into Glacier and (where necessary) retrieve from Glacier. AWS Storage Gateway may be a good fit for your use case.

This documentation on Glacier https://docs.aws.amazon.com/amazonglacier/latest/dev/introduction.html and S3 File Gateway https://docs.aws.amazon.com/filegateway/latest/files3/what-is-file-s3.html should give you more information on the technologies I've mentioned above.

There are no special restrictions for saving PDF files.
I think Amazon S3 is a good choice for long-term archiving of PDF files.
S3 has a storage class called S3 Glacier, which is suitable for long-term archiving.
By using this storage class, you can archive large amounts of data at a lower cost than using regular S3.
S3 Glacier basically takes about 3-5 hours to retrieve data.
Also, since the cost of retrieving data is pay-as-you-go according to the size and the number of requests, storing frequently accessed data will actually increase the cost, so be careful.
https://aws.amazon.com/s3/storage-classes/glacier/?nc1=h_ls
https://docs.aws.amazon.com/amazonglacier/latest/dev/introduction.html