I have a PDF I created on a Mac (“print to PDF” from a PowerPoint), and then reduced the file-size from 21+MB to about 1MB using https://www.sejda.com/compress-pdf .

When I send to people with Macs (and iPhones) using either email or a direct Dropbox link, it opens for them no problems, but PC users are getting an error (file corrupt or invalid file format).

I haven’t come across Mac/PC compatibility issues in years, especially with something as “universal” as a PDF.

Any ideas?

I don’t use a Mac, so can’t really comment on specifics….but the first thing I would try to identify is whether the file is OK before it is compressed by that sejda program.
Can you send the original file to someone to test & if that can be opened on PC? If it can be, then the chances are that it is the compression program causing the problem.

The original is too big for email ops – but see if the PC users can open the uncompressed version via dropbox

Use a native rather than a web tool to reduce the file size. Try Automator first, as it’s free.

Have done further testing. The original PDF (PPT’s export to PDF) is not able to be opened by PC users either (using Dropbox link). So something either in the PPTX or something the Mac is doing on export. Weird. Will continue testing, open to any further ideas!

Oh, I missed the PowerPoint bit.

Is it a font related problem? If you have non-standard fonts, you can embed them into the PDF, but it increases the file size. It could be that shrinking the file size is cause problems with this.

Also, opening the PowerPoint file in Windows and creating a PDF from that, then trying to open it on a Mac might help identify where the problem is.

Does it have a .pdf file extension?

If it’s a recent version of PowerPoint then save to PDF (under Save As) rather than printing to PDF.

The mac pdf system viewer tends to be open files even if there’s a problem, think it’s fairly lax. I’ve had it before. even on the mac, files that acrobat won’t open, the system view would.

not seen it for a long time, but i think it always amounted to font troubles or, just a case of trying a different way of exporting from the original software.

Using Save as PDF (instead of printing to PDF) seems to have done the trick. Strange. Thanks for all the tips!

Does it have a .pdf file extension?

At the end of most of the meetings we do we produce PDF copies of the PowerPoint slides for the delegates. A few years ago I was having trouble copying the files onto USB sticks. They been converted by one of my colleagues and for some reason he’d used his own mac rather than one of the pc’s we had with us. I couldn’t work out what was going on for a while but then I noticed that the period before the PDF extension was not at the bottom of the line but was justified to the centre. I deleted the file suffix and retyped it and everything worked. I’ve never seen it since and have never heard of anyone else having the issue and over the years since then comparability seems to have become far less of an issue but it might be worth removing then re adding the suffix once the original file is on a  pc.