Iphone – File Formats Supported by UIWebView

Use the method - (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType in your UiWebView's delegate to determine when it wants to load resource.

When the method get's called, you just need to parse the URL from the parameter (NSURLRequest *)request, and return NO if it's one of your desired type and continue with your logic (UIActionSheet) or return YES if the user just clicked a simple link to a HTML file.

Makes sense?

Edit_: For better understanding a quick code example

- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType {
     if(navigationType == UIWebViewNavigationTypeLinkClicked) {
          NSURL *requestedURL = [request URL];
          // ...Check if the URL points to a file you're looking for...
          // Then load the file
          NSData *fileData = [[NSData alloc] initWithContentsOfURL:requestedURL;
          // Get the path to the App's Documents directory
          NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
          NSString *documentsDirectory = [paths objectAtIndex:0]; // Get documents folder
          [fileData writeToFile:[NSString stringWithFormat:@"%@/%@", documentsDirectory, [requestedURL lastPathComponent]] atomically:YES];
     } 
}

Edit2_: I've updated the code sample after our dicussion about your issues in the chat:

- (IBAction)saveFile:(id)sender {
    // Get the URL of the loaded ressource
    NSURL *theRessourcesURL = [[webView request] URL];
    NSString *fileExtension = [theRessourcesURL pathExtension];

    if ([fileExtension isEqualToString:@"png"] || [fileExtension isEqualToString:@"jpg"]) {
        // Get the filename of the loaded ressource form the UIWebView's request URL
        NSString *filename = [theRessourcesURL lastPathComponent];
        NSLog(@"Filename: %@", filename);
        // Get the path to the App's Documents directory
        NSString *docPath = [self documentsDirectoryPath];
        // Combine the filename and the path to the documents dir into the full path
        NSString *pathToDownloadTo = [NSString stringWithFormat:@"%@/%@", docPath, filename];


        // Load the file from the remote server
        NSData *tmp = [NSData dataWithContentsOfURL:theRessourcesURL];
        // Save the loaded data if loaded successfully
        if (tmp != nil) {
            NSError *error = nil;
            // Write the contents of our tmp object into a file
            [tmp writeToFile:pathToDownloadTo options:NSDataWritingAtomic error:&error];
            if (error != nil) {
                NSLog(@"Failed to save the file: %@", [error description]);
            } else {
                // Display an UIAlertView that shows the users we saved the file :)
                UIAlertView *filenameAlert = [[UIAlertView alloc] initWithTitle:@"File saved" message:[NSString stringWithFormat:@"The file %@ has been saved.", filename] delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
                [filenameAlert show];
                [filenameAlert release];
            }
        } else {
            // File could notbe loaded -> handle errors
        }
    } else {
        // File type not supported
    }
}

/**
    Just a small helper function
    that returns the path to our 
    Documents directory
**/
- (NSString *)documentsDirectoryPath {
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectoryPath = [paths objectAtIndex:0];
    return documentsDirectoryPath;
}

You may want to look at the QuickLook Framework for iOS: https://developer.apple.com/library/ios/documentation/FileManagement/Conceptual/DocumentInteraction_TopicsForIOS/Articles/UsingtheQuickLookFramework.html

It supports the following formats:

• iWork documents
• Microsoft Office documents (Office ‘97 and newer)
• Rich Text Format (RTF) documents
• PDF files
• Images
• Text files whose uniform type identifier (UTI) conforms to the public.text type (see * Uniform Type Identifiers Reference)
• Comma-separated value (csv) files

More specifically you may want to look at the QLPreviewController: https://developer.apple.com/library/ios/documentation/NetworkingInternet/Reference/QLPreviewController_Class/Reference/Reference.html#//apple_ref/occ/cl/QLPreviewController