There are two main differences between url.aspx, filename.aspx, assetfilename.aspx, and asseturl.aspx
1) url.aspx and filename.aspx are used to modify the asset's url and filename respectively
2) assetfilename.aspx and asseturl.aspx are used to modify the url and filename of files attached to an asset. Examples of attached assets are images or pdfs uploaded from your local computer using
ShowAquireDocuments().