Here's my thoughts on your list of can Commerce do this?

• Attached PDFs to product descriptions - YES. You can add a new Field Type to any Product Type for attaching files. Navigate to Admin > Commerce > Products > Product Types > [ select a Product Type ] > Manage Fields. Provide a label and name for your new field. Choose File from the Field Type drop down. Save the field and proceed through the configuration screens. Now, when you create products, you'll be able to upload one or more files, such as a PDF. They'll be associated with the product. You can then use the Manage Display option for Product Types or Views, etc. to handle displaying them on your Product Display pages.
• Bilingual product descriptions - YES - You might check out Drupal's localization API, though that might be more useful for writing custom modules (I have little experience in localization/translation). You'll probably need two description fields in your database for each product though.
• Associated Products - YES - You'll want to explore Taxonomy. There is no cross-sale/associate products module built yet so you'd have to build your catalog using taxonomy terms along with a catalog in Views that makes use of arguments/Contextual Filters.
• Selling only certain products - I'm not entirely sure what you mean. Maybe you just mean hide the Add to Cart button or certain other fields, like Price, on certain products. This is probably doable without too much pain. You could use the "Active" field or add another field that designates a product as being for display only, and depending on the state of that field, show/hide the pricing/add-to-cart field. Or you could have non-product items as a separate Content Type and have those display alongside your product catalog where appropriate. As is often the case with Drupal, there are often several ways to approach a task.
• Commerce Shipping - YES - See Commerce Shipping
• No Checkout for Certain Products - YES - This should be doable via Rules.

***Note that you should be comfortable using Drupal, Views, Taxonomy, Content Types, etc.

Hope this helps...

John McCormick / NEAR DARK