If you have a 70 MiB PDF file stored in Alfresco and are trying to look at the document details preview, then you might run into issues with the client-side previewer. A 70 MiB file might be simply too large to be viewd within the browser. For one it will take some time to download the file in the first place and then it needs to be rendered as HTML. This can seriously degrade the performance of the browser - or fail if not enough memory / resources are available.
As far as I am aware, there is currently no addon to trim down on large PDF files. If the PDF consists of many pages, it would be possible to create a rule-based transformation that creates a web preview of only the first XX pages (adjustable to a sensible limit). But if the PDF is large because there is a high-res image on the first page, then such an approach won't work - in that case it might be required to either virtually print or otherwise resample the PDF to include less detail. Again, there is no addon that I know that will do this, so it would be custom implementation-
