Can I put an attachment with file on Thank you page?
If you use the redirect url option then you can setup a thank you page of your own that allows you to do whatever you would like but you can’t “assign” and attachment to any web forms regardless of where they are hosted. You can do something like provide a button to download a file though.
@Gregory_Sterner, you can also host your file in Infusionsoft by going to Files > Company Files and uploading it. Then if you right click on the Download hyperlink, you can “Save link address” - that URL can be put behind a button image on your Infusionsoft hosted thank you page.